May I just clarify a few things.
- No latency issues outbound using pingplotter (10ms looks good to me).
- Speedtests were bad over Easter. How about now?
- The issue definitely looks cyclic between the hours of 10am - 2am. Do you shut down any attached equipment outside of those hours?
It would be interesting to see:-
- The results of a TBB speedtest showing single thread v multi-threaded mode.
- The results of a TBB reverse tracert
Whilst the graphs look nasty they could indicate network activity or congestion and why I'd like to see an up to date single threaded speedtest.
It could also be QoS in your router. (Although its odd that its ok at night).
Mine always looks spiky, yet I know the line is fine - its just down to the way my router [de]prioritises ICMP pings.