YOU SAID:

Every poopy time is peepee time but not every peepee time is poopy time

INTO JAPANESE

うんちの時間はおしっこの時間だが、おしっこの時間はうんちの時間とは限らない

BACK INTO ENGLISH

Poop time is pee time, but pee time isn't necessarily poop time

INTO JAPANESE

うんちの時間はおしっこの時間ですが、おしっこの時間は必ずしもうんちの時間ではありません

BACK INTO ENGLISH

Poop time is pee time, but pee time isn't necessarily poop time