Okay so I got this route going
KSFO - KJFK 0900-1740
KJFK - KSFO 1930-2245
When should I schedule the next I was to do SFO to Chicago O hare!
You can't. You need another plane. Unless you find another route short enough to fill in 22:55-7:50.
Anyway I suggest you to don't use the minimum turnaround time for the plane as it lead to delays that lower your company image.
When you edit a route, change the turnaround time till the expected delay is about 1% (look at the attached image).
And use this time also when you schedule more flight for the same plane.
For example you your 1% time is 1:55 and the first flight arrives a 19:00, schedule the next flight to start at 20:55.