My current understanding is that edge weights can not be made time-dependent. Is this correct?
You can’t do time-dependent routing atm, yes: https://github.com/graphhopper/graphhopper/issues/1494
You can do routing with changing weights based on a fixed time (list of weights per edge) or similar.
ah, so the use of lists of weights per edge sounds interesting. Do you have a link to a use case?