I really appreciate the video, I often mix up words that differ by double/single consonants. So, it sounds like a great translation for ~쯤 would be ~ish. Similar usage and formality as far as I can tell. I think these would be pretty equivalent. 두 시쯤에 와. I'll come at 2ish.
I'm Korean. I've never used the shortened form '즘' or seen it anywhere in my entire life. We use '-쯤' or '즈음.' They can be used interchangeably if it means 'the time when.' Unlike the explanation in the video, 즈음 can also be used with a noun. For example, 겨울 즈음(= 겨울 무렵). '즈음' is often used in literary or poetic contexts. Actually, "겨울 즈음에" is the title of a Korean song.
I assume you just mistyped 쯤. But yes it has the same sort of meaning as ish in English. Ish in English is a bit broader though since it can be used with adjectives like "The color is kinda red-ish) whereas 쯤 is for talking about numbers, time and the like
