In Jain cosmology, time is cyclical and divided into two halves: utsarpiṇī (ascending) and avasarpiṇī (descending). In every half-cycle there are 24 Tirthankaras (ford-makers) who revive and teach the Jain path. So the cycle of 24 refers to these 24 Tirthankaras appearing in succession in each half-cycle. Both Digambar and Śvetāmbara traditions agree on the number 24. ( jainknowledge.com)
We are currently in the avasarpiṇī (descending) half-cycle, and Mahāvīra is counted as the 24th Tirthankara in this half-cycle. After this, the next Tirthankaras will appear in the subsequent utsarpiṇī (ascending) half-cycle. ( jainknowledge.com)
If you’d like, you can read a concise explanation about the 24 Tirthankaras and their role in the current cycle here: