Laurie, your 6PM dropout looks suspiciously like there is something either looping your line or creating interference at that time.
If the FTTN connection is using your old telephony connection, you could add an ADSL filter in line with the modem and monitor via the phone output of the filter to see if you can hear any noise etc on the line at the time of the dropout. The official mantra is that you can't have telephony connections on VDSL (your FTTN connection) but I know from experience that VDSL and a telephony connection can happily co-exist.
There may be some diagnostic capabilities in the router configuration that you could use to track down the problem. There is also a nice software utility called Ping Plotter which you can download and run. Pingplotter will ping a specified address (e.g. google dns server at address 8.8.8.8) at regular intervals and chart the replies, it's easy then to see when the dropouts occur and for how long, the plot files can be saved as well.
https://www.pingplotter.com/products/free.html.
It's also worth putting any NBN router on a UPS, a lot of the problems I see with dropouts are caused bu fluctuations in power.