Is IF really working for me?

Hello everyone,

I am a college student who also works part-time in IT so my sleeping and eating patterns are a mess, also I am prediabetic. I have been doing the 20:4 method for a week now, because 16:8 was very similar to the way I have been eating anyway (I rarely ever eat breakfast, 2 meals in a day). The feeling of hunger has been managable (actually I like it), I don’t have the shakes I just feel a little weak sometimes but I haven’t felt the “mental clarity” or the other benefits people talk about. I don’t have a lot of time to workout, I have a set of dumbbells that I lift everyday at home.

• How do I tell if this diet has been working for me? Do I have to eat better (I haven’t really changed my diet, though I have reduced the amount of carbs I eat) and work out, or a week is too small a time window to decide? I know that obviously if I work out and eat better it would be more beneficial, I am asking that will I get any benefits from IF even if I don’t do these things or should I switch up to an even stricter schedule (I am planning on managing my diet next week when I have time to cook my meals)?
• Can I delay my eating period? For example, I usually eat between 14:00-18:00 then go to sleep shortly after. But yesterday, I was unable to eat until 17:00, leaving just one hour of eating time. Should I have shifted my eating period to 17:00-21:00? Is it important for me to eat at the same time every day, or is it fine if I meet the minimum of 20 hours fast time every day?
• Is it okay if I drink black coffee during fasting? I make my own filtered coffee at home using a filter coffee machine and ground up beans. Is it okay to use flavored coffee beans (peppermint, caramel, chocolate, hazelnut) or should I drink coffee only in my eating time?

Thank you for your suggestions.