Personally I would just take as 3 months.I am sure you can get an appointment within that time(even if it does cut it fine within a few days of expiring).BTW once you get your Philippines marriage licence you do not have to get married straight away if you do not wish to.I just done everything from getting local CNI to getting married in my 21 days stay which was tight but fine(I even had a small honeymoon) but there are some who get all the paperwork done,get the licence then return to marry after a few months.good luck