"I will be in your hotel in two hours" means that the speaker will arrive at the hotel two hours after speaking. "I will be in your hotel for two hours" means that the speaker plans to spend two hours in the hotel. If I am in the hotel, I am inside the building.

What does within 2 hours mean?

The phrase means: You may perhaps be called within an hour. You will definitely be called within two hours. There is no implication that your being called within one hour is any more likely than your being called between one and two hours. Or to put it more cynically: the sentence boils down to this.

Is it two hours or 2 hours?

Even if used in the context 2 hours duration, it is not hyphenated. If used in the sense of a follow up you would use an apostrophe, i.e., He was given an appointment in 2 weeks' time.