@literally45-- It can take anywhere from one to two weeks. Mine usually last a week but I do home remedies and I also use antiviral cream.
I heard that there is a supplement at the pharmacy that helps prevent lip blisters and helps them heal faster. I don't recall the name, but it's something that strengthens the immune system. I'm sure the pharmacist knows.
There are also home remedies you can use. Some people dab a drop of diluted tea tree oil. I personally use salt. It stings but it prevents the blister from filling up with fluid and makes it scab over faster. You should also keep your lips moisturized. There are lip balms with pain relieving ingredients.