I got a €60 referral bonus from Revolut over the holidays within seconds of the final purchase transaction being made by the new account holder over the holidays.
They don't. Banks will run payment files in the background over public/bank holidays but they won't necessarily transfer funds until they can make an interbank settlement.
People should also be aware that just because funds appear on your statement doesn't mean they are cleared funds. IT companies like Revolut will either have accepted a financial risk if they give you cleared funds without receiving payment from another entity or will have them flagged as uncleared funds and buried deep in their T&C's will be something to allow them take the funds back if they don't get it paid over from the other entity.
I've not seen any delays, recently opened a BoI account as I am a UB customer and once it was set up I made a transfer from UB to BoI and it was visible the next day. The banks do have a cut off time each day to allow them run their files so if you try and make a transfer in the evening for example, it may not be the next day when it touches down. Some entities such as building societies and credit unions may have an additional day delay as they may not be full members of the relevant clearing.