‘When’ is most often a subordinating conjunction in the iWeb corpus.
WHEN (CS) 8290974 (A2 conjunction)
collocates in the movie corpus:
1 CAME 7116
She came by the hotel when I was leaving and she gave me this for you.
2 COMES 6367
3 SAW 3620
4 GETS 2919
5 STARTED 2636
The next most common use is as a question adverb.
WHEN (RRQ) 2397700
collocates
1 REMEMBER 4680
2 LAST 3690
When was the last time you ate?
3 SINCE 2847
4 HAPPENS 2477
5 CAME 2055
It is also part of a 2 part subordinating conjunction:
EVEN WHEN (CS22) 355663 (unlisted in the English Vocabulary Profile)
collocates:
1 WERE 178
This is where you showed me that you were a loyal friend even when I didn’t have the courage to be me.
2 ALWAYS 72
3 TRUTH 17
4 LAUGH 14
5 WIN 14
Finally, it is also used after ‘no matter‘ WHEN (RRQV33) 3767
Basic principles: No matter what, no matter when, no matter who, any man has a chance to sweep any woman off her feet.
* * RRQV33
1 NO MATTER WHERE 57858
2 NO MATTER HOW 44850
3 NO MATTER WHEN 3655
4 NO MATTER WHY 630