"Let's call it a day. I'm too tired to continue working."
"We can't continue working without Mike, so let's call it a day."
"It's already nine o'clock. Let's call it a day."
A: "How much more work do we have for tonight?"
B: "I think we finished everything for the day."
A: "Good. Let's call it a day then."
Other Common Sentences
"Let's turn in for the night."
"I think we should pick it up from the morning."
pick it up = continue