When you described the situation in your original post I thought it not likely that the problem was your ONT or router. It doesn't seem likely that an ONT/router problem would change with the time of day.
The problem you're having is more likely at the PON, or due to saturation elsewhere in the FiOS system. I don't know that any of your fellow users on this peer-to-peer forum will have a suggestion on how to get Verizon to get with the program, track down the problem in their system, and correct it. I don't have any such suggestion, except to keep bugging support and hoping that they eventually do what's necessary to help you out.
Good luck. :smileyfrustrated: