Shorter time to timestamp while grouping messages

[brianlovin]

Status

• WIP
• Ready for review
• Needs testing

Deploy after merge (delete what needn't be deployed)

• hyperion (frontend)

[brianlovin]

Context here: 6 hours is a long time before adding a timestamp. And even though we add timestamps on-hover, it can make conversations where there are multiple-hour gaps between messages confusing to read, especially in situations where someone might be answering questions or fixing a bug but there's no timestamp to indicate that time has elapsed. One hour is still kind of long but since Spectrum tends towards more async conversations we don't want to get too short here, otherwise every other message will have a timestamp divider.

[mxstbr]

Agree with the thinking, let's see what this feels like!