Uniformize checks based on time?

[laurentsimon]

We currently:

1. signed tags checks for the last 5 tags
2. signed releases checks for the last 5 releases
3. Pull request checks for the first page of commits (~30 last commits?)
4. etc

Maybe we could uniformize them by using a common time window instead. For example we could use the last n months (user-provided option) and set it to, say, 6 months by default.

There are limitations to doing this: in some cases we may find no commits, no releases, etc in the time period.
A more general way could be to have options for users to say 'over the last n releases', 'over the last n months' for a small set of things that would make sense for developers.

This is just an idea. Comments welcome!