I agree with what others said.. no such thing as a dumb question... The dumbest thing you can do is NOT ask.
It's Ok to leave it on overnight. Just like they said, the on/off feature is more for safety.. for instances like when you put it in a pocket, or purse, or whatever where the button might fire without you knowing it. I would turn it off to put it in your bag for work.
Now, depending on the atomizer, you might also want to keep it upright, and preferably in it's own compartment if you have an area for it. If any
juice leaks out, it could get on whatever is in your bag.
And about the charger... What they said before is true. If a USB charging plug was supplied with your evod, take note of how many Milliamps the charger is... you don't want to try charging your evod too fast. I would probably keep it below 1000 milliamps (1 amp).. The thing with the chargers, is the more milliamps it provides, the faster it charges.. but... if you charge a battery too fast, it could vent.
THis is someone using too strong of a charger to charge their ecig at a pub:
Chances are, this was a cheap one, but the problem is very possible.. especially with many 2.1a (2100 milliamp) chargers used for some of the smartphones out.