Yeah. I did it once before I went on LCY-ZRH-HKG-SIN because they allow you to file up to 3 days beforehand I believe.

But honestly it's pretty easy. Sometimes I forget until I land in SIN and I tend to finish the form with the app as disembarkation is occuring and you're waiting for people to faff for their bags. I think if you use the ICA app you could keep your details on file so sometimes it takes less than a minute.​​​