Does this db need to be doing other things while the clock is ticking?
Either way, create a form with a text box on it.
Create an On Open event to make the value of the text box = 5
Set the Timer Interval property to 60000 (60000 milliseconds in a minute)
Create an On Timer event to take the value of the text box and subtract 1. If the result is > 0, put the new value back in the text box and exit. If the result is 0, put 5 in the text box and run your routine.
The purpose of the text box (instead of using a Timer Interval of 300000) is to make it easier to adjust the time.
Providing the process you are running that takes 4 minutes does not prevent the on timer event from firing, it should work fine. If the process does prevent the on timer event from firing, then skip the count down - leave the timer at 1 minute and simply run the process again on the timer event (if the process ties it up for 4 minuntes and then the timer waits 1 minute - there's your 5 minutes).
Some people will wonder why I didn't use the Timer function (which gives you the number of seconds since midnight). I assume this will run past midnight and I didn't feel like fiddling with the roll over. The Time function could be used as well. Also, the Now function would take into account the date, which would level the midnight issue.