If you pay a bill on-line via your current account facility, you are sending the money (same as handing cash over) and thus debiting your account - recipient wilolo get it 2 - 3 days later.
Same process in reverse for refund - donor's account debited but you will receive refund some 2 - 3 days later.
Seem to recall some while ago that the bank transfer time was to be overhauled, to become something less than 24 hours, but, don't hold your breath!
In certain circumstances you can get this delay to work FOR you - some credit card accounts (on line) will allow you to pay online, by entering your bank account detail and amount. This is credited as a payment same day, but may take 2 - 3 days to get taken from your current account. Applies to some other types of on-line account, too. Useful IF you've nearly over-run payment date, or need a couple of days grace when there's more month than money.