It will be a small speed bump for you.
On the dim sum days, just try to make sure that you are calorie intake/output neutral so concentrate on portion control on those days.
During your normal schedule, I’d also recommend eating your last meal earlier if possible because a wider gap between your last meal and sleep time is beneficial.
I do OMAD during the week and more like 14:10 on the weekends. It works great for me because it lets me be more social on the weekends. If anything, changing up the schedule on a weekly basis seems to help with weight loss, at least for me.
One of the nice aspects of IF is it’s flexibility. You ultimately get to decide this based on your goals. But there’s no streak bonus or on going process that’s getting interrupted if you ease, shift, or not fast at all one day.
My personal approach focused on weight loss but still enjoying my life is to not worry about my timing as much on the weekends, though I’ll still stick to it if I can, but still try to eat the same. So like if you’re doing 16:8 with two meals and no snacking you’d stick to that. Go have dim sum and then maybe like an early dinner and be done for the day, or whatever works for you.