@rundocuri- Aquarium cement takes a little time to dry. Typically, 24 to 48 hours are needed to create a secure bond. I would recommend waiting at least a week before you fill your repaired aquarium with water, just to be on the safe side.
You should also keep in mind that since the bond that aquarium cement creates doesn't happen immediately, you may need to use a clamp to keep your broken pieces together until they dry. Make sure to have all of the materials that you will need handy before you start this repair project so you won't have to interrupt the drying process once you place the cement on each section of your aquarium glass.