The reason I would push for 6 o'clock is that sometimes issues arise out of question period, and having only an hour to prepare a motion, between 3 o'clock and 4, is really tight, but having from 3 to 6 gives us time to prepare. Especially if it's a really significant substantive issue, trying to put a motion together in an hour is really difficult.
On June 9th, 2011. See this statement in context.