I visited at the SilverKris Lounge in Terminal 3 at Changi Airport after my inbound flight landed at 2am. Coming at the odd hours seems to bypass what most other reviews have described, which is the lack of seating and crowding. I was able to snag one of the private booths located to the right of reception, and facing the wall so I had no neighbor. This was to be my staging point for my 10 hour layover.
The food spread was okay but what shone was the hot food that was available. Until 2:30am, there were several options but of course the most popular station was the laksa, of which I had probably 3 bowls over my long layover. After that, the staff switched to cleaning the area and opened up again around 0400 or 0430, from which breakfast options were offered. The laksa came back, of course :) There were plenty of coffee and tea options available, too, including TWG Tea. A hidden gem, however, was the bread pudding. I saw a few cups offered and snagged one before they disappeared. It was so good! I made several returns in hopes they would come back but they never did, even as lunch service started. I asked one of the kitchen staff and they said they were out so that was a bummer... but if you see it I highly recommend it!
The bathrooms were clean and the shower rooms were great. The only suggestion I have is offering air conditioning or even a fan in the shower rooms like I encountered at the ANA Suite Lounge in Tokyo, which prevents feeling hot and sweaty as soon as you get out of the shower. Especially as someone not used to the heat, it would have been nice not to leave in new clothes but already drenched in sweat...
The staff were professional and courteous but the kitchen staff were a treat. One of them recognized me coming back for more food and did not hesitate to pile it up. She was a joy. in terms of clearing plates and such, staff made regular rounds all over the lounge.
I do have to say that as the morning approached, the lounge got considerably busier. Until 6am there was plenty of seating but around 8am it was completely packed. it doesn't help that there's still people sleeping on the couches and such, taking up extra room. Most folks left around 10am, however, leaving plenty of seating but not as roomy as in the dead of the night.
I would suggest investing in sleeping pods/sections/rooms to allow people with long/night layovers to sleep, opening up seating for passengers coming in during the daytime.
I'd say say a safe time to visit would be the late morning or dead of night, with the latter especially to get good seating. I can't speak of the afternoon to evening hours as I flew out shortly after noon. But otherwise, a comfortable place to stay (if you can find a seat) with decent food.