Just to clarify, if your TRS claim is submitted midway through the tax year. When your TRS on your mortgage is granted to you, the full allowance will be divided equally between the remaining months of the year.
eg (very simplistic explanation here lads, so bear with me)
Per Month
Mortage Repayment Amount - €900
Interest Value - €500
If claim is submitted and granted in January then the TRS is €100 per month (20% of €500) so your monthly repayments are €800 to the bank.
If the claim is submitted in January and granted in July, then the TRS is €100 per month (20% of €500), but your previous 6 months paid in advance are refunded to you so your actual mortgage repayments are €700 per month until the end of the tax year.
Goodness I hope that makes sense to you!