My experience:
Revenue tickets, J-class, 2x pax, for travel 15 June
Refund requested: 25 April
4 July - I called SQ Customer Service to ask for update, they assured me the refund was in the queue, being processed in flight-date order (said at the time they were still on May flights)
Notification of refund (email with detailed breakdown) received: 9 July
Full refund posted to my credit card account: 15 July

Now I just have some Lufthansa and LOT refunds to still clear!