4.5lbs in a week-ish is a lot! Likely a lot of that is water weight and I wouldn’t expect to keep losing that fast. Most of the time 5%-10% of your current weight is a good rate to lose weight so 1.6-2.8 lbs per week for you. Sometimes you can push It more than that if you’re more overweight.
As far as weird schedules, I used to have a weird schedule in college, so I just made my eating window a flexible 4 hours. If I started at 12 I had to eat dinner by 4. But if I didn’t eat till 4 I could eat till 8. Worked pretty well for me.
I don’t think there’s anything wrong with mixing it up. I’ve never heard that your fasting windows have to be regimented. In fact, I seen one Dr. recommend that we do mix up our windows. Sorry for no reference, I don’t remember the name.
It’s okay to shorten if you need to. Aim for something regular but if you need to shorten it, do it. Live a life. I normally do 20:4, but if something is happening I’ll shorten it but try to always do at least 16. But there are times when I’ll do shorter if I have to. The long run is far more important than any temporary change. It’s not like a magic number unlocks the secrets. It’s just a way of giving your body a break and cutting back.
Mixing up fasting:feeding windows is fine.
Why do you think you should be losing more? How much do you think you should realistically be losing in just a week’s time? If anything, you should expect weight loss to slow down to a more reasonable rate assuming you aren’t doing anything extreme to maintain a -4.5 lb/week loss.