turtles can get stressed pretty easy , they should start feeding in a couple of weeks . 24c is fine for water temp, there not like saw shells and that . they dont come from warm waters , my murry shortnecks water temp is 24c .
My short necks are at around 24 degrees too. What age are yours?
What sorts of things are you feeding them on? As somebody above said, probably just stressed - one of mine stopped eating for a week or so when he was moved into a new tank a while ago. When all settled and he got hungry enough, he went back to eating as per normal.