Timer ?
Any digital cooking timer from a local hardware store will do. They cost about $5.00 and usually come with a clip - if not; glue a clothes peg onto the back and attach it to either your antenna or your collar.

*** Be sure to get one that has a good bell/ringer, that way you never have to look at it - it 'tells you' when the time is up. If you can; find one that beeps at both the 5 & 10 minute mark, now you know how long until you start lining up for your landing.