We already have 7 and 31 (next month). So you just want it to be persistent?

For events, yes.
Either use the one from the session before, or through a configuration option per user.

We already automatically save this setting so the last selected option is restored.

I just tested it with 2.2.17a, and you are right, it remembers the last set interval.

(I tested it before opening this report in 2.2.16 and it didn't work.
There was no entry in the changelog about this.)

You can therefore close this request as fixed.

Thanks :-)