Twickenham will be a cauldron of noise and expectation when England play Fiji on Friday to open the global showpiece.
"We're peaking now for opening night," Rowntree told a news conference on Thursday.
"Data doesn't lie. The guys are in the shape of their lives... hitting pbs (personal bests). We're ready for tomorrow."
Rowntree said Stuart Lancaster's squad were feeding off the excitement and the atmosphere that would only grow in intensity.
"We've prepared well for this game. For our guys it's the time of their lives. On our own turf... 15 million watching on tv at home and millions more around the world.
"We can feel the excitement and support. It reminds me of the (2012 London) Olympics. It simmered and simmered and then it's here and the whole country got behind it. Tomorrow night will show that."
Asked if the hopes of an expectant nation meant more pressure, he responded: "We're pretty aware of the support,. Which teams the pressure is on? They are ready..."
Fiji, Rowntree said, would pose "some challengers across the board".
"Their second row (Leone Nakarawa)... got to keep him quiet, never mind the number nine (scrumhalf Nikola Matawalu). We've done our homework on them. Our guys are a handful as well. They have to stop us on home turf."
England forward Geoff Parling cautioned that the Fijian forwards were more of a threat than in the past.
"They are much better organised and have improved immensely in the past two seasons," he said.
Struggling to pronounce Nakarawa, he described the Glasgow Warriors lock as "one hell of a player".
"If we're not on they'll be a threat. But it's about what we can do against them."
(Reporting by Justin Palmer, editing by Pritha Sarkar)
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