Posy will spend hours underneath the lamp, and quite often her fur gets very hot to the touch.
Plum, on the other hand, tends to leave after he's warmed up. He'll stay by the "fire," say, for as long as it takes to cook a s'more.
While the cats are sunbathing, Dorothy will often jump onto the couch to see what they are doing. She's always worried that they might be eating something which she, Dorothy, should be eating. Here's a picture I took of such a moment. In it, you can see Dorothy is looking rather pensive, like she's trying to think what it is she forgot to do....
I'm sure it will come to you eventually, Dorothy!