Your UK CNI is ONLY valid for 3 months for the Philippines from the date of your interview and process in the UK registry office. If you were marrying in another country, it may be different, but you have 3 months ONLY, remember that 21 -22 days are taken in posting here in the UK before you get it.
When you make an appointment in Phils UK Embassy, they then exchange for a local CNI. You then need to go to your local municiple (Bicol) to get your local marriage licence and (if necessary) do the marriage guidence seminar (at the local municiple). It takes 10 days to get the local licence to marry so gives you time to do the seminar.