I use an egg timer or a G1000
The reason you time your approach is as as described by IO. You start it at the FAF, when the time reaches that dictated by your ground speed read off the approach plate (i.e. say 2 min 22 seconds at 100kts) you execute a missed approach if you don't have the runway in sight.
You also time your departures, in the US your IFR clearance will typically say something like:
"Climb and maintain 3000, expect 10,000 after 10 minutes"
In which case you start the timer on the take off roll, and if you loose radio contact you continue with your assigned clearance - after 10 minutes you climb to 10,000' etc......