I'd skip midsummer - really hot - but pretty much any other time. I went once in February (Luxor), mild and sunny, though it got nippy once the sun went down. (I'm thinking of along the Nile, don't know about places like Sharm.)
Been to Cairo and Port Said in mid February and it was very pleasantly warm, 25*C or thereabouts. The locals were wearing anoraks and complaining about the cold because it was their midwinter!