No, no one can.
My smartass answer is fairly accurate though. Seriously, if I had only one day to dive in Singapore, I'd dive in the shark tank in Underwater world, if you are into that sort of thing. It is possible to dive the waters around Singapore but viz will be well under 2m and there will be little to see even if it was better. Having said that, over a dozen dives there I have seen a turtle and some squid (20 years ago). If you go with a very experienced guide, you may get to see a sea horse and some nudibranch near the occasional coral head. If you are lucky at the time, you will likely only be able to find a shop that dives there on a weekend. By April, most divers head to Tioman, Aur or Anambas in Malaysia for the whole weekend. A difficult trip might also be made to Bintan but that includes a ferry over to Indonesia, getting to the shop, getting maybe two dives a bit better than Singapore and then getting back to Singapore. I would not think that is worth it either.