Bitcoin both uses and mimmics the time-consensus.

Our human timekeeping is based on space stuff. Earth spinning around its axis(day), around the sun(year), and if you are trained you know the exact date and time based on the stars.

The point is that this data source is:

1: not under the influence of any particular actor. No King can move the heavens and earth so to speak.

2: easy to acces. One has only to open their eyes and look up.

3: easy to interpret. sun? -> day. No sun? -> night (go be depressed somewhere else pole people).

So everyone has easy acces to a hard to change source of data that is easy to translate into information. So negatively put: Any attempt on (sustained large scale) discord on time futile i.e. unlikely to disagree. Positively put: everyone comes to the same conclusion, so we agree.