Visa question (Cairo)

Hello Everyone! Hoping someone can help me with a question I have. I was in Cairo last August and September and had purchased a 3 month visa prior to my visit. I am returning to Egypt in just a few short days, the 1st of January to be exact, and will stay little over a month. This time I did not purchase a visa ahead of time because I was told that I could get my visa at the Cairo airport for $15.00 USD. However; someone just told me that the visa's at the airport in Cairo are valid for only two weeks? Does anyone have any insight as to the truth of the matter? If the visa at the airport is valid for only two weeks, can anyone tell me where would I would go in Cairo to apply for an extension, the fee's etc?