DF 'fishing' for "in progress"

it's quite annoying joining a DF, say Crystal Tower for example, only to have somebody 'fishing' for an 'in progress' instance because they don't want to do the whole thing. a lot of times, the 'duty ready' screen pops up, only to have someone withdraw repeatedly. once or twice, fine whatever, but the other night, it happened literally 17 times. needs to be some sort of timer, maybe 1 minute, when someone withdraw from the 'Ready' screen that they can't join an instance to cut down on the 'fishing'