When does the first recruit come back?
The Little Prince's assassin should return at the end of Sequence 3, after completing the mission The Sentinel Part II.
This is so that:
He can advance to level 14 while on the mission. When he returns he will be leveled up to level 15, making him a Master Assassin. Now he can be placed in the Galata district so it cannot be taken by Templars.