With payment initiation, settlement is part of the overall payment process and is dictated by the rules of the national settlement system(s) involved. In the UAE it's the UAE Financial Transfer System (UAEFTS), on top of which sits Immediate Payment Instruction (IPI) network which enables users to make an immediate payment in AED to another bank account in the UAE immediately.
IPI system processes payments up to AED 25,000 immediately, meaning that as defined by the Central Bank of the UAE the payment must be processed and hit the receiver's account in up to 180 seconds from the moment of initiating it. The IPI system is not impacted by the banking hours and processes payments instantly 24 hours a day, all days of the year.
Payments above AED 25,000 will be processed through the UAEFTS and depending whether payment has been made in banking or non-banking hours it might be settled on the same day or next day.