Prague is worth a stop if you haven't been and you'd like to see it. You can see many of the main sites in 4-5 hours. The city is small enough to be walkable for the main sites. The RS walking tour hits the highlights of the old town and new town.
The RS city walk leaves out the Castle area, though. Some might say skip it if you are short on time, but it's an iconic landmark of the city and for some it is worth seeing in person. There's a great view of the city up there and you can walk through it for free, and quickly, if you don't feel the need to get into ticketed areas. Might be nice to add the Castle if you have time. You could walk to the Castle from the Charles Bridge (there's a set of stairs - a lot of them - to get to the Castle from the river side). To save time, if needed, take a tram or an Uber to get up to, or down from, the Castle area, especially if you are using the North or West entrance. Uber was cheap in Prague, and came in handy. Trams also run up and down from the Castle area. If you do the tram, RS suggests buying an extra ticket before going up to the Castle (might be hard to find a ticket machine up there).