Originally Posted by themitchmann
I wouldn't recommend more than a couple minutes, though I've heard of people leaving racquets with only mains overnight (which makes me cringe).
Stringing stresses the frame, so it's best to finish a string job as quickly as reasonably possible.
When I was a member of the USRSA back in the late 80s / early 90s and the RDC just came out the USRSA strung a racket with the mains only and finished the crosses the next day just to see if the DT came out the same. It did the same racket finished in one continuous string and the one with only the mains strung overnight measured the same.
But I do think you should finish it once started.