Don't plan on getting hot food after 7pm and before 11pm.
Currently in the QR lounge now, having a Singapore Sling. I was informed on entry approx. 8:20pm there is no a la carte menu available at that time. No hot food, only the cold buffet.
After further enquires of the staff, was able to discern that the hot food (and menu) will again become available around 11:30pm. Seems catering is airport based and food is pre prepared and delivered to the lounge 3 hours prior to scheduled flights.
Last Saturday I did arrive here shortly after 6:30pm and while there was some issue with food availability, was able to get some of their very nice lamb chops.