FloridaLady

Yes if you divorce, you can technically file I751 at any time and not just within the 90 day window. Are you able to file earlier? I only say that because you have to account for delivery time and the time it takes for USCIS to record your I751 as "filed" and to send you your extension letter. For most people, it's looking like their extension letters are dated about 1-2 weeks after acceptance. Just to be on the safe side, mailing your packet ASAP is the best bet.

If your processing goes beyond the 18 months and you need to travel you can make an appointment and get an I-551 stamp in your passport. If you switch jobs during this time or even after your letter expires you do not have to present your expired green card and extension letter, you can present a DL and unrestricted social security card. Hope this helps.