YOU SAID:

when the cows come home, i'll run

INTO JAPANESE

牛が帰ってきたら走ります

BACK INTO ENGLISH

I will run when the cow comes back

INTO JAPANESE

牛が戻ってきたら走ります

BACK INTO ENGLISH

Run when the cow returns

INTO JAPANESE

牛が戻ったときに走る

BACK INTO ENGLISH

Run when the cow returns