The Afroman very geek guide to recharging alkaline batteries. The very usual caveats about blowing yourself up apply of course.
You can fully recharge a depleted alkaline AA battery all day without problems. I recharged both types of batteries twice, and I would expect them to easily take many more charges. If you care about safety more than I do, attach a multimeter to the batteries and monitor them so they never reach more than 110% of their rated voltage.