« first day (3 days earlier)  last day (15 days later) » 

16:15
In fairness to @VilleSalo, the reference to BS is the Baumslag-Solitar group; it was humor.
 
2 hours later…
18:32
I could've made it a bit clearer I suppose.

« first day (3 days earlier)  last day (15 days later) »