Overnight reply
A reply that came more than six hours later, crossing the small hours — tracked apart from ordinary reply times because it’s a different thing entirely.
A six-hour gap in the middle of the afternoon and a six-hour gap that happens because everyone was asleep mean completely different things, and averaging them together would blur both. An overnight reply specifically flags the second case — a wait long enough, and positioned overnight, that it’s almost certainly explained by sleep rather than by someone being slow to respond. Counting these separately keeps them from inflating (or, depending on the chat, deflating) an ordinary daytime reply-time number.
Example
A message sent at 11:45pm answered at 8:30am the next day is an overnight reply, not a nine-hour delay in the ordinary sense — it’s one night’s sleep, measured in hours.
Frequently asked questions
Why the six-hour threshold specifically?+
It’s long enough that a same-day, awake delay rarely produces it, and short enough to catch most real overnight gaps without requiring the reply to land after sunrise exactly.
Does an overnight reply count toward reply wait time too?+
It’s tracked as its own number specifically so it doesn’t have to — separating it out is what keeps the ordinary reply-time figure from being dominated by sleep schedules.