It sounds like you need to understand how frame rates and slow-motion works. There is real time and that's how we watch things. Slow-motion means that we are slowing down real time. You can do this into ways. Because media players (television, DVD, YouTube, Windows media player, QuickTime player) always play back at a constant frame rate you control the speed of the play back in relation to real-time by putting more or less slices of real-time in your movie. Did you get that?
After effects has a maximum frame rate of 99 frames per second. Standard media players will play up to 30 frames per second and in some cases 60 frames per second. In today's reality 30 frames per second should be your most used target frame rate. If you want to do slow-motion then it starts with the camera. If you shoot your original footage at 60 frames per second then you place that footage in a 30 frames per second timeline timeline will play back every other frame because the frame rate of the footage and real-time are locked. In other words the footage is always going to try to play back in real time. If you had a photo sonics camera the shot 2000 frames a second and you brought it into AE or any NLE it would play back at the maximum frame rate the software supported so your video would not be real time but would instead play slower but not as slow as if you were playing back every frame. The same goes for shooting video at 15 frames per second. Drop that footage into a 30 frames per second timeline and one second of real-time to the camera would be one second of real time in the timeline. You would just see every frame twice so the motion would not be as smooth.
Let's take your 60 frames per second example. If you wanted to play that footage back at half speed you would reinterpret the footage to 30 frames per second. Then drop it in a 30 FPS time line and one second of real time would be two seconds of screen time.
I'll let's talk about Twictor and all methods that you use to change the frame rate of footage in a timeline. As soon as you run out of real frames software needs to make up the extra frames needed to slow down time. It does this in three ways. The easiest is to repeat frames which gives you kind of jerky motions. The next best option is to blend the frames which means to try and composite the two different frames or slices of time together averaging the pixels so the brightness doesn't change and kind of ghosting the changes in the pixel positions. Thank of the hands on a clock. You're looking at a stopwatch so this way pandas moving very quickly and at frame won the hand is straight up but on frame to the hand has moved 10° to the right. slowing this down using frame blending to get three frames instead of to the first frame would be the hand of 0° and the second frame would show you a faded hand had 0° and a faded hand at 10° each hand with about half of the luminosity it hasin the real frames. The third frame would be the original hand at 10°. Does that make sense?
Third and most difficult way is called motion prediction or motion vector prediction that involves a lot of CPU power and may require tracking and masking and all kinds of other techniques because the software tries to predict what is moving in the frame and reposition the pixels to make a better frame from the two frames from the original slices in time. Twictor can be very good at this. So can AE and even Premiere Pro. It all depends on the shot. The limit of how much you can't slow down a shot depends entirely on what's going on in the frame. Can you slow down 24 frames per second original footage so that one second of camera time takes 10 seconds of real time to play back. sure you can, but the quality of the result depends entirely on the shot and the motion in the frame and the pains you went to to try to get good looking footage. The more you try to slow down the more work you have to do in planning and preparation for the shot. When you are shooting slow-motion shoot at as high a frame rate as your camera will allow and then watch tutorials on advanced slow-motion if you cannot get the results you want with the default settings.
I have worked on projects for Boeing where we shot with high-speed cameras running 30,000 frames per second. I have also pushed 30 frames per second (29.97) standard definition video successfully all the way down to one second of real time taking five or six seconds of screen time but it required a lot of planning and work.
Let us know if you have any other questions. Without seeing the exact shot you're trying to work on and knowing precise details of your proposed workflow I cannot give you any better advice than I already have.