I wouldn't know. It's possible that Verizon has such an odd case of network usage, it could be just enough people calling it quits around that time to cut down on a massive buffer of data being queued up between Level3 and Verizon. We'd need to get someone in-the-know from both networks to explain what is up. 100ms of latency on 10Gbps+ circuits isn't out of the ballpark for extreme cases of saturation, especially if the gear is holding a buffer of data. Normally such circuits go to roughly 10ms when they're full (you can usually see this effect when you max your FiOS connection out. FiOS goes to +10ms latency).
Any system that would be implemented in the event that this is shaping and throttling would have a time of day , or a usage scenario aspect to it. I'm sure the providers in the UK do something similar. It would be too much work (and thus much too expensive) to manually flip a switch than to just let your gear do it for you. Sandvine for the longest time here in the US used to do something similar back when Comcast used them. If you didn't pay for a business circuit, you could safely say that if you had certain traffic patterns, a system would automatically nail you with a throttle without any human intervention.
Even then, there is no excuse if this is a capacity issue not to be beefing up capacity. You don't go out and buy extremely expensive backbone rounting equipment, blades, and line cards and forget to build in future proofing. For what it's worth, anything unused is just a depreciating asset in simple accounting.