Most of the truly asynchronous protocols are only probabilistic. (Similar to avalanche). However this concept is very old already(many papers from the 90s discuss it.

If we have some known max delays we can do this:

• The next witness B receives the block of witness A. Since Witness B knows this message needed a max amount of time to be delivered it can produce its block a bit less than 3 seconds from now to approximately follow this schedule.