The clock resets every day at 1pm in my country. If you post or comment during that time, you will be ranked at or near the top of the Leaderboard. However, you need to hold on to this position by posting and commenting fairly consistently throughout the day. Otherwise, you will lose first place.

It is also not just posting. You need to write something that garners zaps from many Stackers. So yesterday I posted twice but came in at 48th place.

On the other hand, my Travel Light was better received, so I attained 11th position & received about 4000 sats.

Hope this helps. Have fun