I saw a drama where 1 episode lasted for 5-7 minutes for couple years ago.
Where can I find some more?
Can you recommend something? 

In the search filter, you can filter by episode count though you can't do anything about a specific episode duration. There's also a web series tag. Web series tend to be shorter than normal dramas, especially in episode duration (some might be short like 2 minutes while others might be 30 minutes). There's a web series tag that you can enter for the advanced search option on MDL.

Some Korean web dramas:

Love Cells 

72 seconds

Choco Bank

Ghostderella

The Cravings

Between Friendship and Love

Wednesday 3:30pm

I would recommend you look through that web series tag in the filter because it has more dramas than I listed and series that will suit your taste better. 

EXXO Next Door is cute and short.

Meow, Secret Boy, episodes are around half an hour & ~ 12 - 16 episodes.

If someone else can help out with the name, there is a really funny one about two guys who start out living next to each other, then with each other, can't remember after that. It is an hilarious, comedy of errors where the girl they like thinks they are with each other. Each episode is about 10ish minutes long.

Check out TVN D Story on YouTube

Also check out Playlist Global on YouTube