Is there an accurate timeframe for how much time transpired during the events of RE5? Hard to tell what time of the day it started at, but at the end of Chap 2-3...it was night...then when 3-1 started it was morning. Not sure if anything later hinted how much time I passed, just something I am mildly curious about.

I'd say 3 or 4 days.

Well, it was daylight at the beginning. Then during the Ndesu fight it was evening. The next day lasted until the ship deck and after that was Wesker so, all in all I would say 2 full days and nights.

I think it's 3 days in total:

Day 1: Intro (morning), Ndesu fight (evening-night)
Day 2: Marshlands (morning), Ship (night)
Day 3: Ending (sunrise).

Bah on your sunrise!!

How could Chris and Sheva continue their mission without taking rests.

I remember on the very begining of 5-3, Chris and Sheva can sit on the chair and say something like "we haven't rest since the mission starts"

Because Wesker was hardly going to wait around for the BSAA to have a smoke and a coffee?

lol.

BTW, did Wesker need sleeps (with his super human strength)?

He might've...but similarly, he wouldn't have waited around whilst putting his plan into effect, would've had more on his mind than having a rest.

Though he had enough downtime during the game i guess to perhaps get some sleep himself whilst Excellla took care of things.

I'm sure that after the Arklay Mansion and Rockfort Island. Chris was more than capable of staying up for two days. Who's to say that Sheva and Chris didn't take turns in driving the boat in the Marshlands, one could have rested for a while, then switched with the other.

Sure it's not sensible, but then again this is Resident Evil. Common sense isn't an issue.