Explicate that FTL is derived from block time (refactoring)
Explicate that FTL is derived from block time (refactoring)

... as
[documented](https://github.com/aeternity/protocol/blame/108d94fc543c79b78a97608d512bba3963f6c6c5/consensus/consensus.md#L377).

aeternity/epoch,aeternity/epoch,aeternity/epoch,aeternity/epoch