Currently, the timestamp specified in the genesis file is used as the timestamp for the first block. The consensus code checks to ensure that the first block time matches this genesis time and rejects the first block if they do not match.

With the creation of the proposer-based timestamps algorithm, this is no longer needed. It was important when using BFT time that the block's timestamp match the genesis time because there was no other possible timestamp that could be used in the first block. BFT time relied on using values form the previous height to generate the next height's timestamp, but no previous height exists during the first height. PBTS no longer relies on values from the previous height, so it should be safe to relax the validation to ensure that the first block's timestamp is >= the genesis time.