Toledo side trip?

Plenty to do in Madrid. I'm not sure the HOHO will be worth it, since most of Madrid's sights are in a pretty compact area. But maybe a good choice if one or more of you have some mobility limitations. Toledo is a good day or overnight trip if you have more time overall in the Madrid area, but you don't this time.

Madrid has plenty to keep you there. Start with Rick Steve’s walking tour. But Toledo is lovely. We took the train there for a day trip. We enjoyed a city bus tour while there. Easy to get lost in those old narrow streets but fun to wonder through. Do not miss the cathedral while in Toledo.

My family and I were in Spain this past April. We spent approximately 72 hours in Madrid. We spent one of the days on an organized day tour to Toledo and saw 5 of what they call the monuments including the Catedral. When we got back, we went to the Plaza de Oriente and Retiro Park. We also went to Plaza Mayor in the morning prior to the tour.
The next day we went to the Royal Palace and the Prado museum in the afternoon.
The following day we had a leisurely breakfast and then took the train to Sevilla.
We never do the HopOn Hop Off Bus nor the RS walking tours as we usually don't have the time. We just pick the sites we want to see and then walk or take a taxi.

Madrid is such a huge city, you will not really get the flavor of Spain there. As much as you would get the flavor of the US by visiting LA. Expect to spend four hours, if not more, at the El Prado. If you have tickets, which are timed, you will spend at least 30 minutes waiting to get in with that reservation. It's certainly worth your time to visit. Though it will cost you more, eat lunch at the Prado Restaurant, not its Cafeteria, if you want to enjoy foods the locals eat. You can get hamburgers at McDonalds at home. No reason to spend a fortune going half way around the world to buy a burger and fries.
Toledo is a suburb of Madrid. Folks commute the half hour train ride each day to and from work so you want to avoid the morning and evening rush hour. Pick a time between 9 and noon if you do decide to go and return anytime after four. You may want to plan a meal, which is the main meal of the day, between 1 and 4, otherwise you'll not be able to get a reasonably priced meal, just appetizers (Tapas). I recommend that you eat the meal of the day lunch at the restaurant in the Alcazar, and don't order the Tapas like a typical tourist. The "Old City" is where you want to visit and your first stop should be the Cathedral. You'll need to make a reservation for your entry. The other attractions that Rick points out in his tour guides and videos are worth while visiting, but on a limited visit you may not be able to visit them given your time constraints.

If you’ve never been to Madrid before consider spending all your time there, but I’m assuming you want to visit at least one of the major museums and the palace.

Toledo is very much worth visiting and I feel it merits an overnight.

Optimize your limited time by deciding which places you want to visit before going over. The order you see them in isn’t that important.

It really depends on the weather also. Toledo is hotter than Madrid.