How to control vibrate (strength, timing, calling)?

Hello,

I would like to build one short, light vibration after after certain minutes of an activity.

How does the general call procedure and the setting of duration and strength work?

I monitor the actual minutes in a variable? How to avoid that e.g. after 25 minutes the vibrate call is processed on Update every time until the minute is 26 (so vibration for 1 minute?)

Thanks