do you have to reset the timer when it gets to run for 24 hours

The timer should only have to be reset if there is a power loss.

no, because you don't have to set the timer or 24 hours, just don't use it at all.

If you select the "always on" setting, you should never need to re-set the timer. As you'll see in my review, I set the Watts to "always on" and plugged it into a portable timer that's more accessible. It's been operating this way for 8 months now, and I've never had to change either timer.