Is it okay to leave iphone 5s ON during the night time? - 1

Will it affect the battery life in a negative way?

No but if you charge to 100% it might be on 99-98 % but if you updated to 7.1.1 it will still be on 100% I have a iPad and iPod on 7.1.1

Yes, I do this all the time and have no issues.

Yes, it is ok
No, it will not affect the battery life