Well here I go starting trouble - 
If you're going to have a timer function, it might as well allow multiple entries.  Don't want one?  Don't enter one.  Want a "Switch Tanks" message?  Set it to fire every x minutes.  Maybe have another timer to reset the DG and check the engine instruments every 15 minutes.  If you're a flying diabetic, set a timer to test your blood sugar or eat the required snack every x minutes.  If you want to get fancy, allow a "countdown" timer, too.  For instance, to review plates/freqs/ATIS 20 minutes before arrival, or the required blood sugar check within 30 minutes of landing.  Maybe allow for 0-10 unique timers.