Just to clarify that the block with proof of time too far in the future is built on top of the parent block.
It is true that nodes have a sense of the current time, but we cannot simply disregard the possibility of someone with a much faster proof-of-time algorithm. Even if we take this approach, we need to define what “later” means, and what happens if in the meantime a chain is formed on top of this block.
An attack of a similar flavour was described in Forks in time, the optimistic verification case. The difference is that there the alleged fork was heavier than the current chain (and there was no specific description of how far in the future the blocks’ PoT are). Here there is one block very far in the future, which means the the chain it may form should really be not heavy compared to the potential chain that could be built on the current tip with the “current” time slots.
We may be able to define some process that takes these notion of (potential) heaviness into account, so we don’t even start verifying the block(s) until “later”, but it requires some thought.