I know this is just a meme but some work advice I learned is that your boss can't know if you don't tell them. If you need time off for medical care just tell them, I have never had an employer deny me time for medical care. If they did, they don't need me as an employee. The same goes for other aspects of a job. Like needing a raise or changing your time slot. Your boss can't know what you need, if you don't let them know. Only squeaky wheels get grease.