They are open pretty late - but its VERY crowded after Illuminations and over the prime lunch hours. For lunch, between the ten minute walk there, the ten minute walk back and a possible 40 minute wait for lunch, its a big investment in time for a burger and ice cream. If you go later in the afternoon or right at 11:00, you will be much better off.
After Illuminations, there is the B&C sprint - people watch Illuminations from near the International Gateway and sprint to B&C once the finale ends. Since the restuarant is so tiny, it doesn't take long to fill.
If you do get a table, you can take the DTD bus and transfer to a PC bus if you want to avoid cab fare.
Perhaps one day Disney will expand this restaurant, since its so popular - or put in a similar venue over on the BW side.
Another thing to keep in mind - the Y&BC pool is pretty incredible - it might turn into an expensive sundae - you might discover a need to stay at the Y&BC if you bring kids through here.