If the expedition doesn't start the next day, my character will have time to finish all his tasks and set off for the islands. I don't know about the training, but it seems strange that the GM would simply offer the opportunity to become an apprentice to a powerful mage.
And my character is also a collector of knowledge about the race, so what can I do now?
So, what's the deal? Will four hours be enough to decide on further actions, or should I give you another day?
He will probably wander around the city first, then go to the island.