Hello!
There is nothing to stop the green-up trigger to work at In-Play, in fact I've just tested it and it placed bets just after the off, no problem. You need to check the program log and the trigger log (the log of the green-up trigger) to see if there are any error messages explaining what is happening and why the bets could not be placed.
If you want to trade out in any case, just before the off, add the following condition:
Market's Minutes before the off is equal or less than 0.5