Don’t count anything less than 12 hours as a fast. Aim for that as a minimum.
You can definitely vary your schedule but if you’re looking to drop weight fast and consistently, you’ll need to fast consistently. My excess lbs came off steadily over 4.5 months but I did 18 hours minimum with some 24s. I had a goal I needed to reach so I could fit my clothes and get back to my normal pre-pregnancy body so eye on the prize and I got there.
As a 20M, you might only need 16 hours to see results, but you’ll reach your GW faster if you just stick with it for a few months and then switch to maintenance fasting.
Don’t drink diet soda fasting or not. That shit is terrible for you. I’d say that regardless of your goals.
Ultimately it depends on your goals and how fast you want to achieve them. Weight loss is about consistency over weeks and months. So not hitting your goals say 1 or 2 days a week over a long enough time isn’t going to matter that much. What it will primarily change is how quickly you get there.
It’s also important what you’re doing on the days you’re not fasting. If you’re just undoing all the deficit you’ve build up on the other days then you’re not going to make progress as well. Again, overall long-term consistency is what matters.
>Will drinks like pepsi max and diet coke slow or stop my weight loss?
Strictly no, but it’s also not that simple.
There was some user who posted a while back who got really fit and apparently was chugging pepsi max by his own admission. Artificial sweetners are tricky things though and they don’t effect everyone the same. And there are different ones which can trigger different amounts of insulin and such in the body. Personally, I found they were making me hungrier and cutting back on my extreme diet soda drinking was a huge help. So something to maybe experiment with for yourself, if they help you get to your next meal without eating there’s an argument in favor of them, but in general maybe have them more as an occasional treat.