I want to know how much time does the game need to play as well as a 2700 rated player on a P4 3Ghz computer. If I set up the game to 1 hour let's say and play against the grandmaster, how good will it be? Is it enough time? or maybe time set here doesn't matter?
How does it work exactly?

Thank you.

The ratings for the personalities are based mostly on computer vs. computer games. CPU speed affects personality ratings, too. CPU speed calculations are performed every time you start Chessmaster, so it's possible to have a personality with a slightly different rating between different Chessmaster sessions.

Time does affect quality of play... obviously, the computer can do a more in-depth search when you give it more time.

well... and how can you explain that in a 20 minute game, I mostly make a tie with the Grandmaster (which is said to be the brains behind the finest chess game in the world) ????

You are either really really good, or your game doesn't function properly.