Not sure on this, I think it has a 3 year validity. My LTO conversion from British licence was secured on 10/7/09 with an expiry date of 27/04/12 - the renewal date is your birth date assuming that you wont forget I suppose. Vehicle licence is of course annual with late penalties.
The only reason I know this is because 4 years ago I converted my licence and was issued a tempory for one year.. After that one year I went back to collect my licence card.. It wasnt there and I was called into the LTO office.. They reminded me that I already had a licence applied for and received sometime in the 90`s.. (I had completely forgotten about it)
They reckoned that the old licence was still current and they worked out that I owed a 3,500 PHP fine for not ever renewing it..
It took them 8 months to issue me a new card!!