Success! Five hours proved to be plenty of time to escape Schipol for an enjoyable Saturday evening in the city before returning to the airport to catch our flight to the UK.
We stashed our carry-on luggage in the lockers located at the airport near the airport train station. A "medium" (actually quite large) locker is € 6 for 24 hours. The freedom to wander the city without carrying around unnecessary things is great.
The inter-city trains run very frequently between the airport and Amsterdam Centraal Station. A ticket costs € 3.70 each way, and the inter-city train takes only 16 minutes. The ticket machines do not accept cash. You can pay with coins or with a bank card--you might want to use the change machine located near the luggage lockers to get some coins. To pay with a credit card (i.e. Visa), there is a small surcharge and you must know the PIN for your your credit card.
There is no shortage of restaurants and cozy, crowded pubs. We did not have any particular place in mind at the time of the arrival, so we enjoyed simply wandering around somewhat randomly, enjoying the scene of dutch families sitting down to dinner in their brightly-lit canalside apartments. (It appears that the transition between the lunch and dinner menus at many restaurants occurs at 6pm.)
By luck we stumbled into exactly the sort of restaurant I had been hoping to find, cozy and authentic, and, by the time we left, completely full of people, in the Jordaan neighborhood. We dallied for a desert course. Loathe to rush our meal, we then had to hurry back to the central station to return to the airport and catch our flight.
Returning to Schipol at 8pm, we found that our flight to the UK departed out of the terminal (D) where the train station is located, saving a possibly long walk to the gate. There was absolutely no line at immigration (I was surprised to have my passport stamped--I thought this didn't happen on intra-EU travel?) and we made it to our gate right on time.