DP said:
It must be filed with AIS in Shannon at least 1 hour prior to departure
And in my experience, they actually make you wait the full 60 minutes
Had to postpone, then cancel a FP from Kerry to Haverfordwest a couple of years back because of a tech problem. Almost predictably, shortly after cancelling the FP, I managed to resolve the problem but then had to refile and wait.....
By the way, tomcs, flying in Ireland is very enjoyable and hassle free (once your FP is accepted).
Aiglon