Technical
Epoch
The precise reference time at which a set of orbital elements is valid; orbit predictions are propagated forward or backward from this instant.
An epoch is the timestamp attached to a state vector or set of orbital elements, specifying the exact moment they describe. Because orbits evolve under perturbations, elements are only accurate at their epoch and must be propagated to estimate position at other times.
Two-line element sets (TLEs) carry an epoch, and the accuracy of any conjunction assessment depends on how recent and precise the underlying epochs are.