If you regularly don’t meet your own shipping deadlines, you should not be selling. It’s irresponsible, it’s rude and it’s borderline scamming. When a buyer pays you, they’re entering a business contract with you based on the terms YOU put in the listing, and you’re breaking the terms of that contract when you don’t ship on time. I don’t care what your reason is; it’s not okay if it happens all the time. List your times accurately so people can make an informed decision when buying.