Device to act as a WiFI hotspot and (small) web server for classroom use?

That's a good point. It may also play havoc with the squid cache to some extent. Might be worth it to consider using hardware that DOES have an RTC.

Or NTP synced. Even if sync lapsed a while ago, as I recall 802.11 requires 20 ppm or better frequency accuracy. As a result, you'd expect better than ~75 ms per hour or under 2 seconds per day.

Edit: 20 ppm for 5 GHz and "only" 25 ppm for 2.4 GHz, but still pretty tight.

I suspect I'd be running openntpd on all the devices (or whatever the smallest packaged equivalent is).

busybox's NTP works reasonably well. Visibility isn't as good as you would have with the reference implementation, but it's small and functional.

If you have the space full-on ntpd and ntpq and the like are available. They aren't so big that they keep me from installing them on my 16 MB routers so that centralized logging is consistent within 10s of ms.

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That's what we do. As "lessons" also to be held in public transport, using 3g/4g connections. rsync everything over night is best "read ahead".

I sent PM to you.