I don’t think it’ll be easy (and I haven’t done this myself), but I think it’s possible using the REST API for two things
- Users
- Posts
You also can do exports of these, but you’d need to do “All time” exports and refresh them regularly.
With a BI tool (Tableau, Power BI, etc), you should be able to link those two data sources by userId. Then, you could create a table that pulls in
- UserId / username
- Registration Date
- Date of first Time Stamp (from the Posts data)
You should be able to also then calculate the difference between those two date and average/median it out.
Could you do the same thing in Excel/Google Sheets? Probably, but there’s a lot more risk of messing things up in the many steps along the way. From my experience, BI tools will make it a lot easier to 1.) model and 2.) refresh.
If you don’t have the expertise and/or tools needed to do that, I recommend finding a colleague who does.