I am still playing around with TTA and finding my way about. Apologies if this has been mentioned before.
The Feed in TTA shows the following for me:
The headings I know about are Today, Yesterday, Last Week and Last Month.
Activities older than one week appear to be considered as last month! I do not consider October 5th to be last month; it is still this month. Last month would, in my opinion, be older than four weeks or physically in the preceding month. I.e. all activities in September would be last month or activities prior to 14th September, either would work but the current display just looks silly and detracts from the professionalism of the application. Something like 'Previous Four Weeks' might be more accurate? I cannot comment on headings for older activities as I haven't been using the application long enough yet.
This is in version 4.22.3 on IpadOS.