As far as I know, such information is not given anywhere on the official website nor ingame, yet. However, Tibiadrome's rotations last for 2 weeks (except for the first rotation). They start (and end) every other Wednesday from July 28 on, when the first rotation will end. The second rotation will end exactly two weeks after that, on August 11th. And so on.
I quickly made the following table with all rotations that will start in this year. I hope it helps!
Rotation | Starts On |
1 | July 12, 2021 |
2 | July 28, 2021 |
3 | August 11, 2021 |
4 | August 25, 2021 |
5 | September 8, 2021 |
6 | September 22, 2021 |
7 | October 6, 2021 |
8 | October 20, 2021 |
9 | November 3, 2021 |
10 | November 17, 2021 |
11 | December 1, 2021 |
12 | December 15, 2021 |
13 | December 29, 2021 |
Edit (July 25th): I created this page on the English TibiaWiki where you can see the current Drome rotation, how long ago it started, and how long till it end and a new rotation begin. :)
Edit 2 (July 26th): I edited my answer as soon as the CMs confirmed the first rotation will exceptionally last for 16 days (Source: CM Skerio post).
Edit 3 (July 27th): With today's patch, the Leaderbords section of the official website shows when the current Tibiadrome rotation will end. Presumably, it will show the ending dates for all past rotations.