No time frame on Allowance but you must retain the property for 10 year.
However, if I am reading your post correctly, you indicate that if you switched to interest only you would have a profit, which indicates that you are taking a deduction for the capital element of the loan. Only the interest element is allowed for this purpose. Additionally, at the very least you should have a PRSI liability after year 1, what it will be will be determained by your PRSI class, unless you have sufficient Capital Allowances (F&F) to write off without using the section relief.