If you can't reach your doctor before the procedure, do not take the medication. It is best to take it with you and ask when you get there. This way if they don't want you to take it, you can, immediately after your procedure.
Your dose from the day before will carry you for awhile into the next day.
You should be asking your doc and the person who is going to control the anesthesia those questions. This is not a questions the lay population can really answer. Your doc and the anesthesiologist will be able to answer it specifically.