One hour is not enough time. The visa process takes about 10-20 minutes depending on how many people are waiting in line (remember, you have to buy the visa stamp first and then wait in another line to go through immigration). Your flight may also require a change of terminal--it seems like every time I go through Cairo, my domestic flight leaves from a different place than the time before. This is not a quick process--one of the domestic terminals is a 10-minute taxi ride away, and if you are stuck taking the airport shuttle, you can wait quite a while for it to show up.

I also find CAI one of the most confusing and least user-friendly airports I have ever been to (and that is saying a lot, considering the places in the world that I travel). There is very little signage that is of any use and almost no information on terminal locations or which flights leave from which terminal. Getting between terminals is very tricky.

I build at least 2 hours into every CAI transfer.