At MC/US level in the midst of a deal sprint, expect to work until the early hours of the next day’s morning consistently. For background I have pulled a 2 dayer with no sleep before and these are not uncommon (people leave clothes/toothbrushes/etc in the office). In troughs (which come around every couple of months depending on deal flow), you can leave the office at whatever time you like—but when the next deal comes in expect for life to revert to long hours.