Sounds like interference or congestion in those hours. Give them a call while it's happening, they are normally quite good at sorting stuff like that out within a few minutes.I've been getting regular performance drops in the evenings for the last couple of weeks on week days. Weekends and after hours during the week it's awesome. For example yesterday YouTube defaults to 1080p60fps and buffers upwards of 8000kbps. Right now no video will go over 600kbps.
I'll open a ticket once I've collected my evidence... Is this happening to anyone else?