Apparently, customers of many banks in the UK can (or will soon be able) to transfer money from their account and have it arrive in the target account (even at another participating bank) on the same day.
I wonder when that capability will come to Germany.
As far as I know, payments are mandated by law to be credited to another account on the next business day, but same-day service isn't that common. (Sometimes not even in between accounts at the same institution.)
I suspect this is a hold-over from the good old days when everything was (is) batch-processed by huge main-frames during the night, rather than having "instant" transactions.