Because of timezone differences these can be easily exploited by people anxious to boost their ratings. Here's an alternative suggestion for people who want to complete a game quickly but don't want to play normal blitz.
Set the blitz timer for 60 minutes per player, nil increments. Then the game cannot run longer than two hours. If this is not enough, ask the administrators to provide the ability to select 120 or even 240 minutes per player.
While this site is mainly designed for turn-based games, there must be others here who would like the opportunity to play games more nearly similar to OTB timing.