When a timestamp is several months old, and we leave
the application around (in a forgotten tab) for
more than three weeks, the usual method of updating
the timestamp fails.

This change works around that by maxing out our timeouts
at 24 days. (This will simply cause us to check the
time in every 24 days.)

Fixes #1952.

I also moved the 5-second minimum to the same time helper.