As far as I understand there’s about a month and three days of delay in the Element’s earning calculations.
If that is true, I don’t get why one of my best earning items (calculated until 15 sept) is a track I uploaded very recently. Actually I have had only new tracks in my top 3 for quite some time…
Can anyone shed a light on this? What am I missing?
Thanks! 
Because earnings are calculated at the end of subscription, and 1st sept + 33 days = 3rd October, so technically every subscription that started from 1st Sept could include your Halloween track.
Hi WormwoodMusic! Each day of Elements Earnings data represents a full month of licensing activity by subscribers who started on that particular day.
For example, when we display earnings for “September 12” we take all subscriptions that began on that date, and look at a complete month of activity for all those accounts. From October 3rd onwards, subscribers could start licensing your Halloween track, so it will start contributing to how much you earn for that day.
Rickyloca is almost correct on the details - we use calendar months for earnings, so the earliest subscribers who would generate earnings for your Halloween track will start on September 3rd. Anyone who subscribed on Sep 1 or Sep 2 will have completed their full month of activity before your track released on October 3rd: if they licensed that track, it would count towards your October earnings.
The 33 day delay before we display item-level earnings is because we need to wait a full month after the last possible subscription period began in a month (in this case, one month from Sep 30th), so we have a complete list of the items they have licensed. We then add a small buffer period to allow for data processing, as there are several systems involved in turning subscriber revenue and item licenses into item-level earnings.
Crystal clear. Thanks for such a detailed explanation! 
