When is the best time to file my I-485 on an O-1 visa in order not to be affected by the 90-day rule?

Although the Foreign Affairs Manual of the U.S. Department of State confirms that having a pending green card petition is not a reason to deny an O-1 visa, the conservative approach is to wait 90 days before filing adjustment of status as the O-1A visa is not a full dual-intent visa like the H-1B visa or L-1 visa.

O-1 is not dual intent so if you file for adjustment, best to wait for the travel permit (called advance parole.)

The O-1 is not a fully dual intent visa, but USCIS has determined that the filing of a preference petition shall not be a basis for denying classification as an O-1 or O-3 dependent. Therefore, it may be argued that the USCIS 60-day rule and Department of State 90-day rule do not apply. If you want to be conservative waiting over 60 days is a good idea, and if you are very conservative, waiting over 90-days makes sense.