There are 2 different fish eyes buff at this spot.

One is 2 minutes precise and instantly displays 1 minute remaining.
The 2nd one is roughly 2min30.

I'm pretty sure Protohropken only bites during the 2 minutes fish eyes.
I just immediately cancel fish eyes if i didn't get the right one.

It worked pretty well for me so far, as it seems i can catch hropken rather quickly that way.