Yes.
schedule("0 "+randomMinute+" "+randomHour+" ? * FRI *", checkForUpdate)
this runs at a random time, this is a direct quote from one that works. But if you wanted to schedule the job to run every 4 mins,
schedule("0 */4 * ? * * *", refresh)
I am pretty sure that would be what you would want.
Or you can simply do runEvery5Minutes(refresh)
or runEvery10Minutes(refresh)
also. There are several different options up to 3 hours I think. But you can't use any number you want.