How to prepare

Hi all, incoming FT at BB in NY. I am thinking about my life for the next few years, seems daunting to be honest. Have had internships before where I finished at 1:30/2am at the latest and was smashed the next day. I don't really mind working from 9:30am - 12am everyday if I'm honest, but those few extra hours absolutely killed. I know what I'm getting myself into, but am just wondering the frequency of 3am finishes, and whether I can tell my seniors that I genuinely cannot work due to my tiredness. Don't want to fall asleep at the desk and get fired lol. Also, realistically how late can I come in the next day? If I get comments at 1am while I am already working on something else, can I ask to work on them tommorrow or will I have to pull an all nighter to finish?

How long does it take for my body to get used to the relentless stress and sleep deprivation to the point where I can take it and it becomes normal? I have been working a very easy job since I graduated early for the past few months, and I feel like this will be a shock to my system. How do I manage/become acclimatised quicker?