When any moment is given a name, it thus becomes irretrievable. There are countless yesterdays and tomorrows, yet there is only one nineteen-seventy’s January, first. One way of avoiding the grief for a timestamp is to stick to the relative timing.
Absolute timing worked well on old static media, such as paper. Inks on the paper shan’t change since printed, just as the timestamp they encode won’t. Nonetheless, it’s slightly harder for humans to decode the absolute timestamp. We always tend to evaluate whether that happened in ancient times, or just an instant ago. Relative timings help here very well: “a hour ago” is always aligned with the intuition of a reader. And new media, such as displays on the computers and communicators can substitute their content dynamically to accommodate to the time passing. What have been shown as “yesterday” yesterday would be “two days ago” tomorrow.
Particularly it is true for chat apps: “last seen at 23:59” could mean numerous different things depending on the context and the time zone gap. Also, this notation adds noise if that “23:59” was a minute ago.
There are always certain cases where absolute timings are the only choice, but, whenever appropriate, try to use the relative ones. Your users will thank you, over time.