Custom constrain: minimum temporal separation of two blocks?

[astronasko]

i want to observe a certain target several times over the course of one night, but I want the observing blocks to be separated by a minimum of some time X (e.g. 6 hours). How would I go about that?

I thought about submitting two observing blocks with the same target, and providing a constraint to the second one.. but I am not sure if the constraint object of the block can "see" the constraint object of another block.