Why are the Jews locked in the synagogue for 24 hours?

The Jews were waiting to board the train to go to the concentration camps.

This is from the book Night by Elie Wiesel. The Wiesel family is moved to the smaller ghetto until the time comes for them to be relocated to the concentration camps. On the day they are supposed to load into the cattle cars they must pass through the synagogue. However, the train does not arrive on time and they are shut into the synagogue to wait. It takes 24 hours for the train to arrive.