I'd go with the Friday. Always best to just go about the day leisurely beforehand, making sure you're nice and sharp. Having practice the day before doesn't make the blindest bit of difference IME, my first two tests I practised the day before and I failed them; the last test, I didn't drive for 2 weeks, jumped straight back in and passed with just 1 minor, felt really refreshed and focused and I drove almost perfectly in the hour before and during the test.