From my dealings with the Irish Authority you need to have your application in with the applicable experience by the end of the 5 years.
If your lacking in the required experience for the B license it might worth getting an A license in the mean time, that's if you have the required experience for it. That way the clock is no more and you can convert to the B license at your leisure in the future, when you've gained the extra required experience. Oh, and paid the appropriate fee.
