I start feeling very weak around hour 25 is that normal ?
If you’re new to fasting, you’re probably not yet metabolically flexible, aka fat adapted.
https://www.marksdailyapple.com/definitive-guide-to-metabolic-flexibility/
I have been doing ADF for over a decade on and off and it’s pretty normal in the beginning. It always takes me a couple weeks to feel really good on my down days. I allow myself 500ish calories if needed because that’s the worst time. Also make sure to add some salted broth or salted lemon juice water, which will help immensely. I just did a 7 day water fast and realized that it was easier than starting an ADF so what you are experiencing is completely normal and will get easier.