If you have done everything right, the screen will probably go until the stencil begins to wear on a long run.
Occasional clogs occur (a lot is dependant on the ink) and a shot of screen cleaner as suggested does the trick. If you get a clog after a short time, and it returns promptly, we'd look for unwashed out emulsion in the screen.
We either bag the screen or cover it, if leaving inked on the press. Maybe we have fine particulate, but it just don't print the same after a few days later for us without covering. Keeps bugs out also. Keeps passing by staffers from poking at it as well. We use trash bags we buy by the pallet and use for other things as well, so cost is minimal.