Absolutely not! If you want time to think, play daily chess.
The ability to stall will be abused and accusations of stalling will be frequent.
Do you really want to play with some anonymous stranger behind a computer screen and spend time wondering if they will ever make a move?
Should they add a no-time limit? I mean it. It would be great to avoid running out of time and have time to think. On the other hand, some random people might just join and be inactive, which could be quite annoying.