Hi!
SO, what are you guys using??
As Ryan5252 already said: There is a timer built into almost every piece of modern avionics (ADF, Transponder, GPS, many NAV/COM units, ...). Many aeroplanes have a panel or yoke mounted clock/stopwatch/timer. Then there's your mobile phone (not only the iPhone has a timer!), your watch, your pocket calculator.
But if you really feel that you need a timer, the cheapest 5€ kitchen timer will do the job as you say!
Good luck with your test!
max