If you want a day that is guaranteed to go uninterrupted it would be Friday or Saturday, issue is a lot of teams already play 4/5 times a week and probably wouldn't want to be playing more, else they would have been scrimming.
It's a tough situation but unfortunately, ETF2L officials > ESL cup. Now you could argue that you could participate in the cup and drop in the worst case if it doesn't mean so much to us anyway as a substitute for pre-game scrims, but some people don't want to play hours of TF2 in a row.
Weekly cups are not sustainable. I'm sure there's other Prem team leaders out there who see the value in them as I do from talking to them, it's just not realistic that each cup will have us signing up to them if we have officials on Sundays, etc.
I think the monthly cups were far better as it is a lot easier to convince the players on your team to play an extra day 1 week out of the 4 weeks in a month. Every week though? It's a hard sell. I can play TF2 all day on a weekend but I see why others on my team wouldn't want to or straight out can't due to other commitments.
Probably should have posted this on the proper ESL thread or the Discord rather than the cre8 post but since there's some amount of serious discussion and questioning on why Prem teams aren't signing up, I thought I'd clarify.
edit: Forgot to throw in that the time is very inopportune. An 18/19 CET start would be most reasonable imo.