Structuring in October detected in AML software and SAR reported in November. Customer structured again this month. File SAR now or wait until January (90 days)?

Why would you file now? Once you file on suspicious activity, a follow-up SAR is only required every 90 days.

^ Agreed. No need to file now Trees. Besides, there may be subsequent structuring events which you will aggregate with one SAR filing with the required threshold.

Yeah, you actually have 120 days to file after your last filing date (regulatory relief). I strongly encourage you to wait out a full 90-120 days.

Per FinCEN SAR FAQs
FinCEN provided clarifying guidance on this question in Section 4 (Page 53) of SAR Activity Review Trends, Tips, & Issues #21. The guidance states “Financial institutions with SAR requirements may file SARs for continuing activity after a 90-day review with the filing deadline being 120 days after the date of the previously related SAR filing. Financial institutions may also file SARs on continuing activity earlier than the 120-day deadline if the institution believes the activity warrants earlier review by law enforcement.”

So, for filings where a subject has been identified, the timeline is as follows:

Identification of suspicious activity and subject: Day 0.
Deadline for initial SAR filing: Day 30.
End of 90 day review: Day 120.
Deadline for continuing activity SAR with subject information: Day 150 (120 days from the date of the initial filing on Day 30).
If the activity continues, this timeframe will result in three SARs filed over a 12-month period.

Perfect, thanks.