I use both ICICI and SBI for my banking needs and I can assure from the transactions history that ICICI holds NEFT funds either inward or outward for atleast a day if not two days before passing on the funds to the beneficiary.
And, they charge Rs 5 + taxes for this facility. This has increased in frequency in the last two months. I would request the RBI to get ICICI mend its ways. I have personally had to reschedule a couple of payments for the banks behaviour. I am not sure if ICICI holds funds for short term interest gains but if the bank is doing it may god save them.
Vamsi