The Official Airport Assistance Network of the World Airports
3-hour layover (airport only): Grab a coffee and a local dish at Atem Alka Café, browse the Perfume Souq in Terminal 3's duty-free, and settle into a lounge if you have access.
5–6 hour layover: With the new shuttle bus services connecting the airport to central Cairo and Heliopolis, a quick loop to see a bit of the city is realistic, with a comfortable buffer to get back.
8+ hour layover: A half-day trip to see the Pyramids of Giza or Islamic Cairo is very doable for a longer layover — just build in solid buffer time for Cairo traffic and re-clearing security on your return.