Garmin Question:
I have a Garmin 235.  I use it on all my runs.  I currently have it set to auto lap each mile.  My wife and I are going to do the WDW marathon in a r/w/r fashion, but probably a bit different than most interval plans.  Our plan is to run to the first mile marker, then walk for 2:30, then run to the next mile marker, then walk for 2:30... etc.  So it's not time/time, or dist/dist.
Without going away from auto lap... Is there a way I can use the watch to count to 2:30 for me each mile so we can know how long to walk?  For our training runs, I'm doing it by Garmin's auto lap each mile.  That means I look at what the timer reads when we hit (for example) Mile 2 and then I have to do some quick math on what the timer would read 2:30 later and just watch to see when we should run again.
I'd prefer to keep my watch on auto lap and figure out a simple way to start a 2:30 counter whenever I hit the mile marker.  I wasn't sure if there might be an app for this that I can download on the Garmin or another simple way.  However after typing all this out, maybe I just need to go to manual laps and simply hit the lap button when we get to each mile marker.  Then I could set one of my fields to be lap time.  Any Garmin Pros care to weight in?
thanks!