How long should the duration of police interviews be?

My answer is “Not more than one hour.”
I say this because an investigation into a case of unlawful assembly (Ms Han was said to be investigated for this offence) is not a complicated case.

It is not one about a murder committed in the middle of the night and the murderer has disappeared without a trace.
In Ms Han’s case the alleged offence took place at our Speakers’ Corner. Here we have to go on the premise that as long as the National Parks (NParks) is notified, the assembly is lawful. The only unlawful assembly I can think of is when those who gathered carried weapons in order to create chaos in the park.
Other than that, we have to start the investigation on the footing that Ms Han and her audience, as long as they had notified NParks and here I am told they had done so, were lawfully gathered at Hong Lim.
So how should the police have proceeded from there? I heard that the police were thinking that the permit to use the park was revoked. Well, whether it was revoked or not, the best witness should be NParks officers, not Ms Han. There should be a document in writing as oral revocation tends to be problematic since NParks is a government department. I am sure those running NParks know that its authority come from someone who will not be stationed at the park. Who represents the department and who has the authority to revoke such a permit would definitely be disputed if there was nothing in writing from a person authorised to issue such revocations. And if at all the police needs to put this issue to Ms Han, her answer would surely be a yes or no. There is nothing to elaborate.
Before Ms Han is called for the interview, I am sure the police would have done all the necessary preliminary investigations and obtained statements from their own force – plain clothes police officers as well as those in uniform who were present at the park on the day in question. They would have access to a great amount of video footages and would have run through them efficiently. They would have gone through the rules and regulations governing the use of the park.
After all, the police officers were on the scene and recorded the whole event from the start till the end, what else can the police know more from Ms Han? They already have on record and the accounts of their police officers.

So if you ask me for my view, I would say one hour is more than sufficient. Anything more than that would be fishing and harassment of a witness.
In passing, I would like to comment on the power of the police.
During the days of our colonial master and until 1984, section 68(2) of the Criminal Procedure code authorised the police to detain a suspect for 24 hours. In 1984, an amendment to this law increased this duration to 48 hours.
Despite this extended period, I noticed that public prosecutors frequently sought further remand of accused persons in court. The presiding magistrate tend to lean in favour of such requests and remand whether it be in a mental institution or in the police station were granted without hesitation.
Today we have computers and not manual typewriters to record statements. Tape recorders or even close circuit surveillance system could be used to record the interview.  Surely the speed of recording has increased tremendously and 48 hours can now revert to 24 hours again.
Having myself been detained for 48 hours and more and being subjected to harsh interrogation, I strongly oppose this practice of the police to detain a suspect for an inordinate period of time. Being subjected to interrogation in harsh and unfamiliar environment is not an invitation to tea. Forty-eight hours is a very long time and many involuntary confessions can result.
The present law does not require video-taping of police interrogations and abuse can, though I am not saying that it happens, take place. I hope the attorney general will look into a revision of this unjust law. While there is a need to protect the public against crimes, there is also a need to protect suspects of crimes for the suspect remains innocent until conviction in open court. The suspect’s human rights too need protection.