Timestamps are used in modding to refer to times or hit objects in a beatmap. When posted on beatmap discussions, they create special links that can be used to easily jump to that point in the editor. 416n48
Copying (Ctrl + C) a selection of hit objects in the editor will put a timestamp on the clipboard. The time in the bottom-left can also be clicked on and copied.
Timestamp syntax: <minutes>:<seconds>:<milliseconds> (<combo numbers>)
Link syntax: osu://edit/<timestamp>
minutes and seconds are padded with zeroes to 2 digits, and milliseconds is padded to 3. combo numbers are optional and separated by commas.
osu!mania hit objects in timestamps use a <milliseconds>|<column> format instead of a combo number. column refers to the zero-indexed position of the column starting from the left of the playfield.
1 minute and 20 seconds:
01:20:000
Hit objects with combo numbers 5 and 6, starting at 12 seconds and 34 milliseconds:
00:12:034 (5,6)
osu!mania hit objects in the 1st and 4th columns at 1 minute, and in the 7th column at 1 minute and 35 seconds:
01:00:000 (60000|0,60000|3,95000|6)