not true. most of the main banks will release within 3-5 days. merchant actually only has 5 days to claim the funds
https://www.sc.com/sg/help/general-information/
SC also mentioned in their FAQ, authorisation hold can be max 15days. I don't know where did you get this 5 days information because I have many experiences that tell me 5 days couldn't be right, I had transaction which merchant didn't claim even though its a valid purchase and it take 2 weeks.