I'm scheduled to land in Amsterdam at 8:20 am and I'm looking to book my connecting flight to Prague at 4:20 pm. Would this give me enough time to head into town for a quick lunch and stroll?
That's easily done. There are frequent direct trains from Schiphol airport to Amsterdam Centraal (at least 4/hr), taking less than 20 mins. A day return ticket is € 8,40, and can be bought at the manned window or from a machine.
Prague is within the Schengen zone, so you don't have to be back at Schiphol before - let's say - 14.30.
yes plenty of time just keep an eye on your watch in case you become to immersed in the city.