Taxing a bike/refund of tax

[BBROWN1664]

My son sold his moped last week and the sale/transfer site is only available 7 till 7. The v5 will only take a couple of days to come through though so crack on and use the bike then tax it when you get the v5.
If the seller goes online to do the "sale" then you can go online to tax it the same day they "sell" the bike.