I have an old countdown clock for windows users that runs independently from any platform. the time period is adjustable (3 min, 4 min, etc.), and the start time is adjustable. I can't remember where I got it from, but I even get it to work on my iMac. I use the "playonmac" app to get it running. it works well. I use it for the occasional odd bar period ( 3 min.). it does suck up some cpu energy though. it is an EXE file type.