My Jeep Cherokee 1998 has been having long crank times on cold starts and rough idles, I've read online that cycling the key for 4-5s fixes the cold start problem, so I've started doing that.
How long will my fuel pump last if I just cycle the key instead of replacing my fuel pump?

 

it will last just as long as it would have with no problem. your fuel pump runs continuously with the truck running. When you go to key on it energizes the fuel pump relay for 2 seconds...that primes the fuel line and a check valve holds pressure for long enough to get the engine to running...that keeps fuel pump running. The check valve is in the pump housing assy...IN THE TANK. Your priming trick keeps the pump running for 15 seconds longer than usual...so what.

 

Cycling the key is just masking the problem your fuel pump is already weak. It could last weeks or months, but it’s dying. The longer you wait, the higher the risk of it failing completely (often at the worst time). Replace it ASAP cheaper than a tow truck. Check the fuel pressure regulator too while you’re at it.

 

Measure the pressure on your fuel rail - if its tow replace the pump. If it's within specs, check your plugs, rotor, cap and sensors