Held after the women's time trial, the men too face a 50 percent chance of rain and changing winds, a likely deciding factor.
The 54.5km course consists of two laps of the Grumari circuit that formed part of the road race. Each rider follows the 2.5km flat coastal road before reaching the 24.7km circuit they must complete twice before the Copacabana finish.
Largely flat, the first section takes in some lumpy road including a small section of cobbles. These stones created panic during the road race and as a result, a recent strip was paved for riders to avoid the rough surface.
Riders then turn inland up the Grumari climb which averages 9.4 percent over 1.3km. The first 600m are relatively easy but a steep section with double-digit gradients, peaking at 24.1% will cause pain before the climb flattens near the top.
A technical descent then follows, difficult on TT bikes especially on slippery, wet roads.
Each time trialist then faces an 8km section of flat roads before hitting the Grota Funda climb which averages nicely at 6.8 per cent over 2.1km.
Then it's just the descent to the coast to complete the circuit. But where the women will stop, the men do it all again.
Overall, the course has long, flat sections for the powerful riders, a steep, punchy climb as well as a regular, shallower one and some technical sections. As with the women's race, a complete rider will win gold.
So, who can win? The usual suspects, but it hasn’t been smooth sailing for any of them.
Tom Dumoulin (Netherlands)
Dumoulin was the big favourite after his win in the first TT of the Tour de France and second in the subsequent mountain TT.
A rider with the versatility to take on the punchy Grumari climb and power away on the flats, Dumoulin was the clear go-to star. Until his crash on chaotic Stage 19 left him with a broken wrist.
The Dutchman withdrew early from the Olympic road race and said he still suffers significant pain in his wrist. But his form is good ahead of the biggest target of his season. Pain he may suffer, but the main test will be if his he aerodynamic time trial position is at all compromised.
Chris Froome (Great Britain)
Tour de France champion Froome was unable to keep up with the best in the Olympic road race but he is a lot better suited to the effort against the Rio clock.
He split the time trials with Dumoulin in the Tour, smashing the mountain TT. His TT second to the Dutchman in stage 13 may have come down to the wind picking up mid-stage and affecting riders starting later.
Froome won’t be bothered by the ascents, even if the Grumari climb is a bit punchier than he normally prefers.
The real test will be whether he can back up after a very tough Tour de France and Olympic road race.
It is worth noting a Grand Tour TT can be a very different beast from a one-off event and is as much about recovery as power and Froome won’t have the advantage of tired competitors here.
But he is one of the big favourites to medal and add to his bronze the London TT.
Rohan Dennis (Australia)
Dennis has built his entire season around his tilt at Rio Olympic gold. In comparison to his rivals, he's had a less disrupted path to the Games. He did crash during training, taking off some skin but this shouldn't affect his medal pursuit.
The main question is if his form is good enough to overcome the big names present. He was a minute and 41 seconds behind Tom Dumoulin in stage 13 Tour de France TT. His only two victories in TTs in 2016 have come without competing against the big names.
With his focus entirely on the Olympics, his lesser form against other riders during the season may just peak in time to beat the best against the clock.
Dennis is a strong medal candidate he will certainly be supremely motivated after sacrificing much of his season to this one goal.
Tony Martin (Germany)
The Panzerwagen is an acknowledged powerhouse against the clock but is a bit more limited in tackling the climbs.
If the race was entirely flat, he would be a top favourite, but once a few climbs and technical sections are thrown in, more versatile riders rise above the big German.
That said, the climbs aren’t very long, so Martin isn’t entirely out of this one. If he can limit his losses on the ascents, there is plenty of long, flat sections where he can get into his rhythm and put the power down.
His form this year hasn’t been great with only a single victory in nine attempts this season. Then again, it’s rare he’s far off the mark.
A darkhorse for this one? Feels wrong to say of the Panzerwagon but he’ll have to be a lot better than his recent form to win here.
Fabian Cancellara (Switzerland)
Spartacus is looking to cap off his stellar career with a win on the biggest stage. A win here will be the highlight of his season, which has already seen him take six wins, including Strade Bianche.
The four-time world champion against the clock hasn’t been a consistent winner against the bigger names of the discipline recently. But he has still performed consistently without the wins of recent years.
He exited early from the Tour de France to hone his Rio TT preparations, a signal he’s keen to do well here. That level of focus from Cancellara is often the precursor to a top-level performance so it would silly to expect less from ‘Spartacus’ in Rio.
A win for the 35-year-old may be a bridge too far at this stage of his career, but a medal to add to his Beijing gold and silver is realistic.
Vasil Kiryienka (Belarus)
Kiryienka was a surprise winner of last year’s World Championship TT, emerging atop of upside-down podium showing-up the big contenders.
It would be an even bigger upset for the out-of-form Belarussian to win a medal in Rio.
He hasn’t been a factor in recent time trials and it would take a pretty stunning form reversal to medal.
But It is worth noting he always does better in these one-off TTS than in races against the clock in multi-stage events, especially at the 2016 Tour de France where he worked doggedly for Sky team-mate Froome.
Julien Alaphillipe (France), Andrey Zeits (Kazakhstan), Primoz Roglic (Slovenia), Ion Izaguirre (Spain) and Taylor Phinney (USA) are other riders that could spring a surprise, probably not for the gold medal but none of them would be out of place taking a medal of some description.
Men's Time Trial Start List
All times are in AEST and scheduled for broadcast this evening across the channels/platforms of network 7.
11pm AEST 37 NAM CRAVEN Dan
11:01:30 36 ALG REGUIGUI Youcef
11:03:00 35 TUR ORKEN Ahmet
11:04:30 34 IRI MIZBANI IRANAGH Ghader
11:06:00 33 MAR LAHSAINI Mouhssine
11:07:30 32 VEN MONSALVE Yonathan
11:09:00 31 RUS KOCHETKOV Pavel
11:10:30 30 ARG SEPULVEDA Eduardo
11:12:00 29 DEN JUUL JENSEN Christopher
11:13:30 28 AUT PREIDLER Georg
11:15:00 27 FRA VUILLERMOZ Alexis
11:16:30 26 UKR GRIVKO Andriy
11:18:00 25 GER GESCHKE Simon
11:19:30 24 USA BOOKWALTER Brent
11:21:00 23 KAZ ZEITS Andrey
11:22:30 22 ITA CARUSO Damiano
11:24:00 21 CZE KONIG Leopold
11:25:30 20 POL KWIATKOWSKI Michal
11:27:00 19 BEL WELLENS Tim
12:15am 18 NOR BOASSON HAGEN Edvald
12:16:30 17 CAN HOULE Hugo
12:18:00 16 GBR THOMAS Geraint
12:19:30 15 FRA ALAPHILIPPE Julian
12:21:00 14 SLO ROGLIC Primoz
12:22:30 13 ESP CASTROVIEJO NICOLAS Jonathan
12:24:00 12 BLR SIUTSOU Kanstantsin
12:25:30 11 POL BODNAR Maciej
12:27:00 10 CZE BARTA Jan
12:28:30 9 POR SANTOS SIMOES OLIVEIRA Nelson Filipe
12:30:00 8 AUS DENNIS Rohan
12:31:30 7 ESP IZAGUIRRE INSAUSTI Jon
12:33:00 6 USA PHINNEY Taylor
12:34:30 5 SUI CANCELLARA Fabian
12:36:00 4 GER MARTIN Tony
12:37:30 3 BLR KIRYIENKA Vasil
12:39:00 2 NED DUMOULIN Tom
12:40:30 1 GBR FROOME Christopher