This is the 3222nd most frequent Polish word.
sobotniego
"Of Saturday"
sobotniego is used here in the genitive case to describe the specific time or part of Saturday (afternoon).
W sobotniego popołudnie pojechaliśmy na wycieczkę.
On Saturday afternoon, we went on a trip.
sobotniego is used here to indicate a specific part of Saturday (morning).
Sobotniego ranka spacerowaliśmy po parku.
On Saturday morning, we walked in the park.
sobotniego describes the adjective form related to 'Saturday,' used here in the genitive case to describe 'dnia' (day).