I think the question needs to be divided into TWO scenarios:
HOLDING a dose can cause INR to "Drop like a Rock" in one day.
INCREASING a dose will take 3 or 4 days to be fully metabolized.
FWIW, while I agree that getting test results the Same Day is the IDEAL, next day is not catastrophic, especially if you take your meds in the Morning and can wait until the Lab / Doctor's Office is open to see if you need to change dose.
'AL Capshaw'
