Custom constrain: minimum temporal separation of two blocks?

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.

The issue names no files, tests, or entry points. Start by tracing the observing-block and constraint APIs, then determine how separate blocks are represented during scheduling. Done requires an agreed approach for expressing and enforcing a minimum separation, with its behavior documented and tested.

Written by the indexing model from the issue text.