You can shave the day of a spray tan but you should shave at least 12 hours prior to having the spray tan.
If you shave and then have the spray tan too soon after the shaving then it can irritate your skin.
So if you're having a spray tan and want to shave before the spray tan you should make sure you shave at least 12 hours or longer before the spray tan goes on.
If you shave immediately before the spray tan your skin will become irritated from the spray tan product.
So just shave 12 hours or more before the spray tan.