YOU SAID:

Goes to the shops for (supposedly) 15 mins. Comes back 3 hours later.

INTO JAPANESE

店に行くと（たぶん）15分。 3時間後に戻ってきます。

BACK INTO ENGLISH

Go to the store and (hopefully) 15. Will be back in three hours.

INTO JAPANESE

店に行くと（うまくいけば）15. 3時間後に戻ります。

BACK INTO ENGLISH

Is that if we do this thing right,

INTO JAPANESE

うまくいけば、

BACK INTO ENGLISH

Is that if we do this thing right,