Is there a quantum-safe time lock?
A similar construct to a time-lock puzzle is a verifiable delay function. They have a similar notion of "inherent sequentially". They have an unrelated "public verifiability" property which you do not care about.

Boneh et al. build verifiable delay function from a construct called ``Incrementally Verifiable Computation'', which they can instantiate from certain SNARKs/SNARGs. There exist lattice based SNARGS, which I imagine are post-quantum.

I have not checked if all of these notions line up to directly give someone post-quantum VDFs (and therefore post-quantum Time-Lock Puzzles), but this seems like an excellent candidate for what you're looking for.