It's exactly two seconds before I honk your nose

[flamboyant lad]

It's from the movie "The Mask"

Mask says it to someone: Look at that! It's exactly two seconds before I honk your nose and pull your underwear over your head.

Could anyone please tell me what "part of speech" is "before" in the above context & what does it mean?

I think it's used as conjunction.

 

[SwissPete]

It means that I will honk (whatever that means) your nose in exactly two seconds.

 

[Florentia52]

I would say "before" is a conjunction here.