Module Incremental_kernel.Incremental.Make_with_config.Before_or_after

at time returns an incremental that is Before when now () <= time and After when now () >= time + alarm_precision. When now () is between time and time + alarm_precision, at time might be Before or After, due to the fundamental imprecision of the timing wheel. One is guaranteed that an at never becomes After too early, but it may become After up to alarm_precision late.

after span is at (Time.add (now ()) span).