help with trigger - to lay & then back later at 10% better price

Good morning all,

I have been watching closely some non-handicap markets the past 2 weeks & believe there is some value in laying 30 minutes before the race.

So I want to do following:

    * 30 mins before race lay the selection for £10 at best price available
      If matched, I then place a back bet @ 10% better odds
      If unmatched when market goes in play, then try and back @ 10% better than     lay odds



Would welcome some advice - which sample trigger might be a good place for me to look at?

Many thanks