With being generally within that one hour slot; and having gone on for " years of signal dropping out every day", suggests the possibility that it may be something within your own home; and if so, then it is your responsibility to trace etc, not Openreach/BT.
Do you have anything that switches ON particularly in that time slot, eg night-storage heating, someone working a "back-shift" and switching on an oven or even a TV set, on arrival home, showers (very heavy electrical loading - about 8 to 9 KW, compared to a typical 1 bar fire of 1 KW; or TV set at 125 Watts)?
It could also be a neighbour, particularly if you are in a rural situation with long electricity supply lines.
Do lights flicker simultaneously?
Try doing the Quiet Line Test on your phone line during the day a few times, to get an impression of noise levels, then immediately after those drop-outs, to see if there are any differences.