Normal for internet to be throttled during the day?

Hello again, I signed with JCom and have had them for less than one week. They installed cable for me while waiting for construction for fiber. I was pretty content since speed test was showing over 600Mbps down, but yesterday after 1100 the speed and latency went down. Latency went to over 100ms, down has been under 1Mbps making the internet completely unusable. Tried resetting modem and unplugging it with no difference. Around 17 or 1800 yesterday it was resolved, but today same thing is happening after 1100. Is this a normal part of internet here? Or is this just an issue with JCom? Feels like I'm being ripped off if I can't use the Internet for anything during the day.