I’m not sure if the “difference within range” constraint type should be checked on qualifier and reference snaks.
If we go with the “sibling snaks” solution (or whatever we call it) in T175562: Check “conflicts with” and “item requires claim” constraints on qualifiers and references?, we can also use this abstraction to check “diff within range” constraints, e. g. to assert that “end time” as a qualifier is always later than the associated “start time” qualifier (range [0, ∞)).
What do you think?