You can't use a flip to disprove that.
But I can try with words.
Interesting word game, and indeed; the concept of time is man-made. But that man-made system is a way, not of saying here is here at this point, but of measuring how long did it take for this to happen after that. It is not a way of saying this is the 28th of march, and it is a wednesday, and we are at this orbital position; therefore this should happen. No, it is more a way of saying that, and asking how long ago it was since these exact circumstances last cropped up.
It is like meters and/or yards. They are man-made systems of saying how far something is from something else. Just like our concept of seconds; except on a different dimension.