How Long Should my Girlfriend and I Stay at Myrtle Beach?

We live in Michigan and the airplane ride will take us two hours to get to Myrtle Beach. I was planning on leaving around noon on a Friday and coming back on Sunday at around 4 PM. But now my gf is considering leaving Thursday at around 6 PM and coming back on Sunday at around 4 PM. For the people who have been to Myrtle Beach, what do you think is the better option? Do you think that we will give ourselves enough time for the trip if we leave on Friday instead of Thursday?