Just a regular speedo will do, like the Trail Tech standard speedo. For a clock you can pick up a wrist watch from Wal-Mart. Make sure your watch has seconds and minutes displayed at the same time. I use one as a back up duck taped on top my bar pad.
If you can come across a stock modern KTM speedo (the skinny one) from ebay you can program it to show mileage with tenths and real time clock with seconds at the same time. But they are expensive and rare.
You might even be able to pick up an older generation enduro computer. I'm still using an 80's vintage ICO Pro3. It handles speed average changes, mid race pauses, etc.
Once you get all dude-ed up with timekeeping the best thing to do is get to the start line and pick some other smart looking bloke with some enduro equipment and just cue off him. We call that time leaching. Try to pick an 'A' rider. Nothing wrong with it as long as you don't get in his way.
Just ride and have fun.
- c bob
Dream House Family Fun Ride - May 3, 2009
Dream House 500 Adventure Ride - October 3, 2009
to benefit the Dream House for Medically Fragile Children