I've got a Cygolite Night Rover with NiCad battery. The run time between charging depends on whether you use the bright beam, low beam, or both. On low, it will easily last more than 3 hours, perhaps 4. With both lights on, perhaps 2+ hours.
With NiCad batteries, I think it is best to run down the batteries as low as possible before recharging. I generally charge mine overnight. I think it has some sort of regulating device so the battery won't overcharge, but you don't want to leave it hooked up charging indefinitely. If you are using your light for one hour every day, you should be able to go at least 2 days between charges -- longer if you use the low beam only. Check at the Cygolite website for more details.