usually my rule is to give dramas 4 epsiodes

but in answer to your question

twice.

bride of haebaek - yawn

imaginary cat - WTH is this nonsense????!!!!!!!!!!!!!

NO WAIT

thrice:

kill me, heal me.  the way this drama treats mental illness is heavy handed and nonsensical AT BEST!  i didn't even finish ep 1.  i could not take one second more of this clap trap
While I've only recently started watching Asian dramas, it seems pretty universal to me that the longer a show is the slower it'll also be. When I'm on the fence with a series, I prefer to give it a full quarter of its entire run time. But me being undecided is actually pretty rare. Most of the time, yes, I feel like I can determine whether I'll like a show or not within the first episode.