First an aside to note with relief that I seem to have got Tapiriik working again just before I derailed. Phew 
Now I have set “Max safe days” to 5. Currently graph is showing 9 days 10 hours until derailment.
When does beeminder do this recalculation?
1: When I refresh the graph or dashboard (appears no)
2: When the text data gets fetched (I thought I had set the max safe days before the last fetch, but not before the date of the last activity - so unsure on this)
3: At midnight? (ie the daily deadline)
4: Something else?
Dave