In Book 13, when Athena and Odysseus discuss their plan and strategy for overcoming the suitors which will enable Odysseus to regain his rightful kingdom of Ithaca and his faithful wife, Penelope, Athena says that she will disguise Odysseus so that he will not be recognised. However, at no point does she indicate how long this disguise should be worn. It is hinted by her talk of the violence that she anticipates Odysseus will carry out on the suitors that it will come to an end when Odysseus has had a chance to survey the scene and work out a plan for killing the suitors. Note what Athena says to Odysseus in the following quote:
I will not lose sight of you when once we set about it, and I would imagine that some of those who are devouring your substance will then bespatter the pavement with their blood and brains. I will begin by disguising you so that no human being shall know you; I will cover your body with wrinkles; you shall lose all your yellow hair; I will clothe you in a garment that shall fill all who see it with loathing; I will blear your fine eyes for you, and make you an unseemly object in the sight of the suitors, of your wife, and of the son whom you left behind you.
It is clear that this disguise is a temporary measure whilst Odysseus takes stock of the situation and ascertains how things lie in Ithaca and how much support he has. It gives him a chance to plan his next move in safety of being recognised and thereby triggering a confrontation with the suitors before he is ready for it.