Vtec220

Hi there - there is an HKS turbo timer fitted to my 93 WRX, which I can`t get working right. Sometimes after I turn the ignition off the timer continues to run the engine for 1 minute which is the current setting - however, there have been a couple of times the timer only runs the engine for 5 seconds before switching off. Don`t think the timer has an auto setting on it, could be wrong though. Does anyone know why this might be happening and how to sort it out?. Thanks a lot guys.