After a bit of research this is what I've found out, as I suspected as at work (I work in the day in a law firm) we regularly transfer funds from one side to another, such as a court settlement, in our instances a normal BACs transfer is 3 days (usually 2 days in reality), it can be done same day but they costs an administrative fee. In a home banking capacity, my experience is that if it is a transfer of funds between different banks, it can take up to 24 hours for it to appear in my account, such as when client pay me for photography invoices and they send it online direct banking transfer. If we bank in the same bank, it can be quick, otherwise, it normally appear later that night when I get home.
Anyway. From google.
All inter bank transactions are held through RBI.
1. The senders bank will send the details to RBI on regular intervals. I think, twice in a day.
2. RBI forward that details to receivers bank on regular intervals.
3. The receiver bank then check the validity and formalities.
4. Send the acknowledgement to RBI.
5. Send the details to senders bank and get the money.
6. RBI Send the money to the Receivers bank
All these will be done on bank working hours only.
So if you ordered outside banking hours via Paypal, like 4am then it won't get processed until 9am, which could be way down the list after all those CC payments had gone through.