Vatican Tours

With any tour you can stay longer. The tour ends in 4 hours but you can stay as long as you want (or until the Museum closes). They will not kick you out.

Most tours I found are done at 4 hours and you have to leave the
Vatican

As far as I know that's not true IF the tour ends within the museums. If it ends in St Peter's, then you can't re-enter the museums.

Keep in mind that Vatican City is more than the museums; it also includes Piazza San Pietro, the basilica, the gardens + some other sections which require guided tours, and parts which the public are not allowed access to.

Is there a way that you can stay longer and then go see St Mark's Basilica (without crazy lines)?
Also, are there any tours that are longer than 4 hours?

Are there any tours that are longer than 4 hours?

I'm not aware of any (maybe someone else is). If you want a longer day, at your own pace, you might want to just rent an audio guide or purchase an in-depth guidebook at the entrance. More than 3.5 - 4 hours would be a long time for a tour at a single attraction.

then go see St Mark's Basilica (without crazy lines)?

You can leave the museums and walk 15-20 minutes or so to the basilica entrance (it's St. PETER'S, not St Mark's). Security-check queues can be lengthy but move pretty quickly, and may be shorter later in the day if wishing to do it after the museums.

In addition, I believe one forum poster (Jay in Chicago?) said they'd purchased this fast-track ticket w/audioguide from this resource (link below) but I haven't seen mention of it from anyone else.

https://rometoolkit.rgi.ticketbar.eu/en/ticketbar-rome/st-peters-basilica/

One thing you might consider is doing the museums and the basilica on different days so that each one could be your first stop of the day. I visited the Vatican before it got ridiculously crowded (especially in the museums) and have no recent experience there, but others have spoken highly of the early-AM tours that get you into the museums before they open to the public. They include Walks of Italy's "Pristine Sistine" and at least one offering by the company Dark Rome. There may be others as well. They will help for the first part of your time inside, but eventually I assume the mobs will catch up with you. I suspect that the crowding in the museums (once the public hours begin) will be such that won't want to stay as long as you are expecting.

Several people here have mentioned a comparatively pleasant visit to the Vatican on the night it is open late, so I'd check into that if I couldn't take one of the early-access tours.

Don't forget that the Borghese Gallery requires timed tickets booked in advance. From all reports, it is a much saner museum-going experience than you'll have at the Vatican Museums.

All very good ideas, acraven, but a glance one of the OP's previous posts leads me to think they're traveling during the winter? The museums only have the late openings on Fridays during the warmer months (April - Oct), and not all sections are accessible.

"Pristine Sistine" is very highly rated by RS folks who've taken it but it does end in the basilica so no backtracking to the museums. I suppose one could leave the tour before it exits the Sistine and into the church, though.

They absolutely could do the basilica on a different day if they didn't mind returning to the same part of the city.

If you did want to stay longer after the Pristine Sistine tour you could probably arrange it with your guide and then just give the headset back to them before they exit out of the chapel to go to St. Peters. Several people left at this point in our tour but part of that was because we got sardined and separated in the chapel when all the exits were closed. Others have said that they have used the tour exit that dumps you into St. Peters without actually being on a tour. I don't know if you could plan on that when I was there it was just such a mess that they were trying to get people out of the chapel any way they could. You might also consider a private guide but that would be pricey.

Thank you everyone for your replies! It appears that if we want to see the Basilica that day, we'll need to go back into the Vatican another day.
One more question- I had already booked the 10am City Wonders Vatican Tour as they had a good sale on and were one of the top providers on Trip Advisor. Does anyone have any experience with them? Are we better off with someone else? Is 10am too late of a time to really get much out of the tour?

Ten am is prime time, expect crowds at that hour. If you can go earlier, it will be better.

It appears that if we want to see the Basilica that day, we'll need to
go back into the Vatican another day.

That all depends on how much time you want to spend in the church? It opens at 7:00 AM so if you were there at that time, you'd have several hours to explore before heading over the the museums for your 10:00 tour. It's very possible that there may not be much of a line at all as it'll still be fairly dark outside (sunrise at 7:37). Maybe someone who has been there over a New Year's weekend can weigh in there?

It would make for a very long day if you intend to spend many hours in the museums, though

I've no experience with the City Wonders tours (they have multiple types for the Vatican; no idea which one you booked). I'm also not sure what getting the "good" of a 10:00 tour means? The museums are open until 6:00 PM - they start clearing the galleries at 5:30 - so you'd still have plenty of time left after (what I assume is) a 3-hour tour. A big reason some RS posters have preferred the early-entrance tours offered by, say, Walks of Italy, The Roman Guy, etc. is to have a crack at the Sistine before it gets just nuts in there.