Was there recently twice and was told categorically that ANY stay requires a visa... in my case it was just the $25 VOA so no problems at all.... but it seems the 24hr visa free idea is not actually the case. If it IS I have no idea how one gets the immigration people to accept it!

P.S. There are PARTS of Egypt that tourists are strongly advised to avoid...but Cairo is not one of those! Australias Department of Foreign Affairs and Trade (for example) says of Egypt as a whole "Reconsider your need to travel" but it is only for Sharm El Sheikh that they advise "Exercise a High degree of Caution" and for areas within 50 km of the Libyan border/Governate of the Sinai the advice is "Do NOT travel" I would take those last 2 seriously myself. Like others in this thread I felt quite safe in Cairo and environs... irritated by the number and persistence of touts etc...but not unsafe.