The frame rate you set for recording video does not affect the time it takes the video to playback unless you change the frame rate interpretation. In After Effects, you select the video in the Project panel and use the File/Interpret Footage menu. Changing the frame rate there changes the time it takes for a video to playback.
When the footage's frame rate does not match the composition's frame rate (or sequence in Premiere Pro or any other video editing app), frames are repeated.
Lower frame rates increase the likelihood that slow-moving objects will judder or appear to move unevenly. Twenty-four FPS has a standard shutter speed of 1/50 of a second, and that motion blur creates a very similar motion blur to that of the average human eye. 30 or 60 FPS can also have a slower shutter speed.
Your eye tends to follow motion, but if your shot causes the eye to focus on something stationary in the scene and something moving through the foreground with very little motion blur, it can cause a distraction that detracts from the story you have to tell. In most cases, creating a 60 fps video has little or no advantage over a 30 fps video to the viewer. In some cases, it looks less cinematic and does not create strong emotional responses from the viewer nearly as well as footage at 30 fps with a little more motion blur. That's why almost all feature films designed for the big screen are still shot at 24 FPS with a shutter speed of about 1/50 a second.
When you drop 30 fps footage in a 60 fps comp, you will get two identical frames in the timeline by default. If you speed up or slow down the footage in the timeline, there are different frame blending options that you can choose to try to make the footage look better. The different frame blending options are most useful when you slow down footage.
One other thing you might want to consider. All popular streaming and social media services will re-compress your footage and deliver it based on bandwidth. A 4K 60 fps video on YouTube will be shown to most viewers at 1920 (had) and 30 fps because of the bandwidth restrictions. I almost never deliver 60 fps video to a client, but I do deliver a lot of 4K.
One other thing that may help you. If you are shooting footage that needs to be rotoscoped or you are shooting for keying (greenscreen), it is almost always a good idea to reduce the shutter speed to remove motion blur. I usually shoot 30 fps at 1/120 or even 1/250 of a second, create my mattes or keys, and then let the software (AE) simulate the motion blur using Pixel Motion Blur so the motion in the frame becomes more cinematic.
I hope this helps. Most filmmakers who did not get their start shooting with film cameras don't have a real good understanding of frame rates, shutter speeds, the effects of motion blur on the shot, the panning speed of the camera, or the subtleties of moving the camera to create a strong dramatic shot because it is so easy to shoot video. When I first started, creating a simple panning shot that you could not stand to watch because of Judder was very easy.
Sorry about the long answer, but maybe it will give you something to think about.
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