You don't indicate where you are planning to purchase the tour - for simplicity sake, I will assume that you plan to purchase the tour through the official ticketing website CoopCulture where they offer tours in Italian, English, Spanish and French. At the present time, the only tours offered through CoopCulture are of the Colosseum only and do not include the Roman Forum + Palatine Hill. In that case, yes, you can purchase one of their Colosseum tours and then stay afterwards and visit the general admission areas of the Colosseum until it closes for the day around sunset.

It is preferable to book your tickets + tour in advance. The issue with waiting and trying to use one of the "guides" on the spot - how do you know that the guide is genuine? Because there are some scammers outside as well and they will be happy to sell you fraudulent tickets which are worthless - you queue up in the security line and when you reach the gate, you find out the tickets don't work and that you gave your money to a scammer. Much easier to prebook through the official ticketing website CoopCulture. At the present time, there are three different tours offered in several different languages.

We got tickets which allowed re-entry within 24 hours. The Colosseum took us the whole afternoon and there were a lot of people. It was amazing though we opted out of the more expensive tickets which would’ve allowed us into the inner lower depths of this magnificent structure. The following afternoon, we spent a lot of time at the marvellous Forum not realizing that the Palatine closed at 4:00 PM. So we missed the Palatine and only saw it from a distance. We typically don’t rush through history and it’s monuments. And also, we make sure not to miss major meals so we keep our energy level up. Soak in all the sights and sounds and enjoy the grandeur of the old empire. I’m unlike some friends who’ve been lucky to visit 4 times.

The issue with Tiqets or other such websites such as Viator or GetYourGuide is that there is usually another company that lists the tickets on these websites. So unless you reveal the name of this other company, the recommendation is pretty useless because there could be multiple companies listing the same tickets on Tiqets - some of them good, some of them bad. In fact, there was a very sketchy company that listed Vatican Museums tickets on Tiqets, Viator and GYG. They basically demand that you pay extra money on the day of visit. So I would be very, very, very careful about buying Vatican Museums tickets on these websites. In fact, I would probably just buy a breakfast or lunch ticket option on the official website vs buying from Tiqets, Viator, GYG, etc. But if you want to press your luck, be sure to do your homework. Determine the hidden company name that is listing the tickets and make sure you aren't buying from the sketchy one that extorts money from you on the day of visit.

Hey, if you have a look on a site called tiqets, they have lots of different options. I used them for our tickets and the handy app means they are all stored on your phone.

Anyone can purchase the Underground tickets although tickets usually sell quite briskly after they are released

The ticket release schedule was changed due to COVID-19. At the present time, most tickets are released on a rolling 30 day release. So tickets for mid-May would be released in mid-April.

Be aware that the lines on the free admission days can at times be several hours long depending on when you queue up. You can access the audioguide via your smart phone through the official app Parco Colosseo. The last time I checked, it cost 3 Euro if you buy through the app.

If you have already booked your tickets, the only queue that is left is the security line. The security line doesn't normally take too long unless there are a lot of people with backpacks / bags that need to be scanned or manually inspected by employee. If you want to arrive a little earlier to make sure that you find the proper entry point for the Underground, that is fine. In the past, a few people have showed up at the wrong entry point and missed their entry time. I personally would try to arrive between 20 - 30 minutes before your time slot.

Marc: The first option includes an English tour; the second option is just an escorted visit. Whenever you see the words "didactic" or a language (English, Italian, or Spanish) in the description, that means it is a tour. And the tour is extremely affordable - only 10 Euro extra. They changed the ticket release pattern with COVID-19. Most tickets are released on a rolling 30 day in advance schedule. There is a smaller secondary release at the 7 day mark.