I had to check as I was rather blandly observing the departures board recently waiting for my evening flight, and only saw the JNB flight (in my tired mind trying to work out what time it would arrive with the time zones - things you do when bored in airports!).
There is a Delhi/JNB&CPT/MOW&IAH at 02:30 - then nothing until 06:00 - over a 3 day period on the Changi Airport website, so don't think there is anything else unless very sporadic?