When's the best time to go outside and see the stars

Me and my sister have decided it would be fun to go outside and look at the stars tonight but what time would be the best time to?

I'd say around midnight. This is when Earth has radiated most of the heat it collects during the day back off into space.
You mat find this helpful: http://cleardarksky.com/
Also download Stellarium, a free planetarium program: http://www.stellarium.org/

Good luck!