How many creatures can step through a Teleportation Circle before it closes?

The party has just rescued 100 slaves. How many of them can conceivably enter a teleportation circle before the spell ends? It seems absurd to think all 100 can make it.

The teleportation circle spell description states that:

A shimmering portal opens within the circle you drew and remains open until the end of your next turn. Any creature that enters the portal instantly appears within 5 feet of the destination circle or in the nearest unoccupied space if that space is occupied.