Ipod Charging Question

My Ipod Nano has been dead for several days now. I just plugged it into my computer to charge it a few minutes ago. I want to go to the gym & I'm getting impatient. My questions are...

How long do I need to let it charge to get about 2 hours of use?

Will it hurt anything if I take it off the charger before letting it fully charge?

Thanks :)