A duração é de 8 horas ou até que a criatura contida por ele escape.
Anteriormente, a descrição diz:
The creature is restrained there until the spell ends.
A restrained creature can make a Dexterity saving throw at the end of each of its turns, ending the effect on itself on a success. Alternatively, the creature or someone else who can reach it can use an action to make an Intelligence (Arcana) check against your spell save DC. On a success, the restrained effect ends.
Portanto, dura 8 horas, mas isso pode ser reduzido se ativado e a criatura salva ou escapa.