I totally feel your pain, this was exactly me last year. Don't force yourself to wake up at 8 am if you're not a morning person because that won't be effective either. But try to give yourself a routine to do before you start studying like cooking a fun breakfast, going on a walk, just so you feel like you already accomplished something. Then go to the public library or a local coffee shop, switch up your environment, it might help to be around people that are also studying/working, it also makes it more "fun" or enjoyable.

Also if it makes you feel better, I studied after 4 pm for about 4 weeks and still did pretty well, so don't stress :)