Seems like a really bad idea. In online Dominion, a major contributing factor to how long your turns take isn't how long you take thinking, it's what strategy you choose. Hamlet/Library is always going to take a long time, whereas playing Big Money is fast. (That's physical time, not number of turns to win.)
That's a serious, serious difference from your example of chess. In chess, regardless of what strategy you pick, the physical manipulation of chess pieces is always going to take roughly an equal time for you and your opponent. In chess, the time restriction is ONLY on how much time you get to spend thinking about your moves. In Dominion, the amount of time making decisions may, depending on the strategy, be smaller than the time actually implementing it (and some strategies may involve more or less decision-making - unlike in chess, where each player makes one move per turn). Trying to claim that the situation is analogous to chess is disingenuous.