The only difficulty I can see is the potential difference between when you start it and when the first match is. But fwiw I'd go for Day 1.
Yeah, I thought about that, but I'd rather start at the beginning than right at the end. And there don't seem to be arguments for delaying once the season has started.
FC Bristbury
Season 5, Level 5
League Winners Levels: 1, 2, 3 & 4
Champions League Winners Levels 2 & 3 Double X 2 (League and Champions League), Levels: 2 & 3