On the same airport wifi mobian bookworm on Librem 5 timezone was updated correctly, on flx1 I had to manually choose timezone. Location services are enabled. I have noticed it works on my laptop debian sid when I use a vpn.
I could not verify this with a vpn connection (timezone was not switched when activating vpn - on laptop timezone switches once vpn is active). Does it give preference to time from the mobile tower/network? Ideally it should and fallback to ip based timezone only if mobile network is not available. May be for additional privacy, we could make this a setting to prefer timezone from the ip address.