For the last few weeks, I've been doing two rides a day about 4 days per week (chipping away at my accumulated vacation days because I'm retiring in a few weeks). Average of 3.5 hours in the morning, then home for the hottest part of the day, then 1.5 to 2 hours in the late afternoon. It's an easy way to avoid the various problems I'd otherwise encounter doing rides of 5 to 6 hours or more.