Lose internet at the exact same time every night

Hello,

We have been in our house for about 7 months and had no issues until about a month ago.  Every night at exactly 9:03 we lose Internet/experience extreme slowness for about 1 hour.   Websites load extremely slowly or not at all off and on during this hour period. There will also be periods, a few minutes at a time where it works perfectly.  Speed tests, when we are able to connect during this period, show up fine.  The lights on the modem and router show no indication of a problem.  It almost behaves as if cox was throttling my bandwidth or something huge was downloading clogging my connection, as far as I know nether is the case.  We have called cox multiple times, have had a tech out and had our own audio video person out to no avail.  We have replaced both our router and modem.  Our router is an AirPort Extreme so I am not sure how to show any logs.  The level 2 tech support suggested it could be interference from neighbors so we tried changing router Chanel's and that did not help.  Cox has said everything that they can see shows no problems.  I am out of ideas other than changing ISPs.  What could be causing service issues at the exact same time every night?  I am not an router/modem expert and I have a pretty complicated set up involving a control 4 set up by professionals.  The control 4 people have told us there is no issue with any of that equipment nor would it cause this type of problem even if there was.  I just don't even know where I can turn for help at this point.  The professionals we have talked to cannot even hypothesize what the problem is any more.