Daily logged-in users count inaccurate when cron is delayed

[Richard Mansfield]

The query uses CURRENT_DATE, but should count logged in users with lastaccess relative to the time the cron job was started.

I suspect there's a delay in cron_site_data_daily because it counts disk usage first (very slow) before it does logged-in users, so if it starts at 23:51, it might skip over into the following day before doing the logged-in users.

We should rewrite the logged-in users query to either hardcode the time the function starts (or just use CURRENT_TIMESTAMP - interval '1 day').

We should also move the disk usage check to happen after the user counts.