Change before storage because used oil contains "acidic" contaminants caused by normal combustion that only a chemist can explain. It will sit in clean oil and be ready for start and go when the time comes. In time it's going to drain down from everywhere that has a passage to the pan and make for a dry startup. Pull ignition coil or otherwise make it crank a bit without starting for say 5 seconds, wait a moment and do again.. don't overdo it...but get the oil at least moving in right direction before you actaully start it and then don't rev it.. allow warmup before you take off.