Unless you’re picking the car up on a Sunday, then I can understand why you’re concerned about the money having to clear 48 hours in advance. It will probably be OK but there remains the possibility that they could go out of business in the interim.
As others have already suggested in this thread, when buying cars from dealers or traders I pay the deposit on credit card and then pay the balance on debit card, bank transfer or CHAPS on the day as agreed with the dealer in advance.
That does require their accounts department to be open - or someone with access to their bank account to be available - to confirm that funds have been received, but that shouldn’t be an issue if agreed in advance and on a weekday.
On one occasion, despite assurances from the bank, a CHAPS payment didn’t go through until the end of the day when the dealers accounts team had gone home (Friday). They took me home, got someone to check overnight and collected me at 0700 the next morning to pick up the car.
If you decide to pay the balance by debit card or bank transfer (using your bank’s mobile phone app) then it’s worth calling them in advance. Depending upon the risk/value they will either do something to allow it through or advise that it will be stopped and a verification call made.
Years ago they seem to preauthorise unusual payments but in recent times - perhaps because of their exposure to fraud - they wish to verify all large transactions at the point it’s made rather than only those above a threshold.
. So far the experience has been friendly and professional.