Assisted some folks at a pattern contest this past weekend for the down-timer to be turned on when throttling up. No more timer buttons to forget to press. However the SPS is a powerful tool for other applications other than timer starts. Any case:

You select code 87 timer function, select down t (for down timer), scroll to Start: select SPS0.

Now, what is SPS0? I stands for "stick position switch". This is a nice capability that allows you to turn stuff on and off with the stick position.

To activate this SPS0, go to the System Mode (holding the ent while turning on the tx), Scroll over to 91 (STK PosSw) and change INH to THRO. Its already set up to POS 0 on when stick is moved to high (turns on the timer when throttle is moved past half throttle). You can adjust anywhere on the stick you want the timer to start, but this is the default setup.

No, go back to code 87. scroll down and set your time (e.g., 10 minutes)

If you want the timer to start when you advance the throttle, and not pause when you move below half throttle (i.e., stay on all the time) then scroll down to "One Time: OFF" and select "OFF" to "ON". Now basically when you plug in your battery or if glow, when you start your motor, the timer won't activate until you go past half throttle (like engine run up or during takeoff). You will hear it beep and its starts counting down at that time, with no other action required on the pilot's part.
Also, Troy Newman has a long blog on this function at his site if you want additional details. site at http://www.patternflyer.com/troy/