At our GP, you have to phone on the day, at 8:30am, and if you don't you won't get an early appointment, you'll just be SOL(s*t out of luck), and have to try on your next free day.
After my last appointment, last Tuesday(which was my 2nd day off; I tried on Monday, but, called after 8:45am. Not a snowball's chance!), I went to the reception counter and said that I had to make an appointment for my smear, as soon as, because of my work schedule and my biological schedule, that was fine, and I got an appointment for 9/9. What happens??? Aunt Flo came in for her visit this past Thursday.
She's always so random! So, now I'll obviously have to call on Tuesday or during the week (our GP isn't open on the weekends. Don't get sick on the weekends in our town, apparently!) and let them know.