DaveE

Wow deja-vu. My wife and I had much the same issue. My wife's former husband was a married man, (of course she didn't know at the time). After three months he left for parts unknown. After he had left she obtained a CENOMAR on him, and it showed his other marriage. Although she knew about it she could not afford to do anything about it. When our relationship started four years ago she was up front about it.
Well I started to pursue how we could get this thing taken care of. First off, how long it takes depends on where the wife is living. Annulment proceedings in Manila seem to take much longer than in the "Province". Many folks try to file in the province to speed things up.
However, the first thing that the court does, is have the "fiscal" (filipino name for prosecutor) certify that you are not forum shopping to expedite or make your annulment easier. Bottom line is that ours took about 9 months, much of it mandatory wait times. She will go through the normal annulment process: pretrial, judge, court date etc.
Things that slow the process down.
1. Mandatory certified letter from the court to the last known address of the bigamist husband informing him that he is being accused. I think he has thirty days to reply
2. If no reply, then publish the impending court case in a filipino newspaper of general circulation for two consecutive weeks.
3. File the certified copies of the newspaper article with the court at the end of the wait period.
4. The court will then schedule your "pre trial". There you present evidence to the court showing why you should be annuled. The fiscal will agreee or disagree with what you present, and certify that there is no evidence of collusion between the parties.
5. Wait, wait, and wait longer to get your case on the court calendar.
6. Finally your court date arrives and all the evidence is heard formally.
7. Wait, wait, wait again for the formal decision. Ours took more than six weeks after the case.
8. Again publish the findings in the newspaper. This time only for one week. This is to provide time for appeals
9. If no appeal then after 15 days the court will render its final decision
8. After the final decision you must register the decision with the Civil Registrar where you live, and the Civil Registrar where the marriage took place. Both of those entities must send you formal letters stating that this has been done.
After all of this, the court will issue the Decree of Annulment stating that the marriage was null and void from the beginning.
Then you can start the process of registering with NSO to get a clean CENOMAR.
Best of luck to you
Dave

Wait a minute. People come here and ask for advice based on other peoples experience and knowledge. Just because something did, or did not happen to you, does not make that advice or experience invalid.
My wife and I went fully prepared for our AOS interview, a ton of documents and photos. We were confident because of what we had read and learned here. The fact that OUR interviewer didn't look at any of our documents and only asked one question is irrelevant. MOST people get asked for lots of relationship proof. Just because we weren't doesn't make the advice to be prepared irrelevant.
This is great forum and we should appreciate it. You want a lawyer's advice, hire one?