My understanding is if you are not making mortgage payments for three months you won't get the trs during that time (since the trs is taken by the bank automatically from whatever your monthly payment is, if your monthly payment is zero then your relief will be zero)
However when you begin paying again you may be entitled to a higher rate of trs since it is an annual relief, i.e. 10,000 euro in year one etc. If you paid 10,000 euro over the other 9 months you would still be entitled to claim 25% of that amount.