i have a theory about the minhyuk + changkyun story in dramarama PLUS a bit about hyungwons role
what if the reason why minhyuk travels back to the past is because changkyun died and he wants to bring him with him to the future (hence why he was holding hands with him while attempting to use the watch again before the men in suits ((like time police or some shit)) stopped them). like the two of them are childhood best friends but changkyun ends up dying somewhere along the line, so hyungwon gives minhyuk the chance to find an alive changkyun in the past and time travel into the future together and basically revive him. thats like, the only reason i could think of that would require time travel to reunite minhyuk + changkyun.
as for hyungwons role, i think hes like the original time traveler (the one who started it all and invented the time traveling watch) thats giving people a chance to save their loved ones that unfortunately, passed away in the past.