Article 24 Vienna Convention on the Law of Treaties

Entry into force

1. A treaty enters into force in such manner and upon such date as it may provide or as the negotiating States may agree.
2. Failing any such provision or agreement, a treaty enters into force as soon as consent to be bound by the treaty has been established for all the negotiating States.
3. When the consent of a State to be bound by a treaty is established on a date after the treaty has
   come into force, the treaty enters into force for that State on that date, unless the treaty otherwise
   provides.
4. The provisions of a treaty regulating the authentication of its text, the establishment of the
   consent of States to be bound by the treaty, the manner or date of its entry into force, reservations, the functions of the depositary and other matters arising necessarily before the entry into force of the treaty apply from the time of the adoption of its text.

See also: Article 23 Vienna Convention on the Law of Treaties