Maybe a (non-internet) TV, or even a smart (internet-capable) TV being turned on for that period? Possibly not even yours, it could be next door's. Also, not necessarily the main home TV.
My broadband basic info/help site - www.robertos.me.uk.
Domains, site and mail hosting - Tsohost
Connection - AAISP Home::1 80/20. 200GB. Sync 71307/12780Kbps @ 600m. BQMs - IPv4