YOU SAID:

The party starts when I walk in

INTO JAPANESE

わたしが来たときパーティーはもうかなり進んでいた。

BACK INTO ENGLISH

The party was well along when I come.

INTO JAPANESE

わたしが来たときパーティーはもうかなり進んでいた。

BACK INTO ENGLISH

The party was well along when I come.