Time lapse is made by recording fewer pictures every second but then play them at regular speed, so say your time lapse is recorded at 1 FPS, then there will be 30 seconds of actual time in every 1 second of your video file played at the normal 30 FPS, and so viewing the file played back at 30 FPS it will just be a second to watch but it cover 30 seconds of actual time.
On the other hand Slow motion, you record say 120 FPS but if you again play those at 30 FPS, your 120 frames recorded in 1 second of actual recording will take 4 seconds to be played at 30 FPS and so it is as it time move slower.
If you playback 120 FPS recording at 120 FPS, then your video will just be the 1 second long and appear to be in a normal video / time speed, your eyes will just not be able to register that many frames in a second.
Many cameras and phones for that matter record directly to a slow motion file, but you can also record one second at 120 FPS and then in a editor sow it down as much as you like, 4 X will be really slow then lasting 4 seconds, but you can also just slow the one second 120 FPS down 2 X and then have a 60 FPS output video, that will be smoother but then the output file will just be 2 seconds long and only half speed slow motion.
So to sum up you can slow down slow motion and still have smooth footage, but you can not speed up time lapse footage and make it look good, all you can do is to make every frame appear 2 or more times in a row to stretch the footage out over actual time, then it would be slower but it would still look very bad. as the subject still move a lot in between every frame recorded. BUT ! you will then have more time to see every frame, but then you might as well use a regular media player software and then just skip 1 frame at the time back or forth, and then grab the actual frame you want.
But like i say most media players can play frame by frame by pushing some button, and then when you are at the frame you want you can grab it and save it as a picture pressing some other button.
What buttons to press to advance or go back 1 frame or take a screen grab depend on the player you use.
