Authentication refreshes while we're in pm_active. The effective
authentication timeout is therefore the idle time in pm_active plus
AUTH_TIMEOUT_MS.

Idle time in pm_active is 10 s at login and default, 30 s at peruse,
so we use 331, a value >= 330 s.

To be perfectly precise, we should subtract any idle time we may have
spent before reaching __DEAUTH, e.g., while holding a button, but
that's nitpicking.