With respect, I disagree, not you but IS.
They are doing something and every day at around 5pm its back on.
I can assure you, without fail when that clock hits around 5 or 5:30, the floodgates open again
Are you sure that's not congestion at your exchange?
I had the opposite issue - my line at 5pm would just drop - living in a residential area only means that that's when people start loading my exchange...