Answer :

it means to stop whatever you are doing and go rest, go home, sleep. 

Answer    :end a period of activity, especially resting content that enough has been done.

"we were prepared to do another long march before calling it a day"

synonyms:

admit defeat · concede defeat · stop trying · give up · give in · surrender · capitulate · be beaten · despair · lose heart · abandon hope · give up hope · throw in the towel/sponge · drop one's bundle

Explanation: