周日 + Time/Activity
周日 (zhōurì) is a noun meaning "Sunday." It is a formal way to refer to the last day of the week in Chinese. For example, 周日下午 means "Sunday afternoon."
我们周日一起去爬山吧。
wǒmen zhōurì yīqǐ qù pá shān ba.
Let's go hiking together on Sunday.
这家店周日不营业。
zhè jiā diàn zhōurì bù yíngyè.
This store is not open on Sundays.
他打算周日下午去看望奶奶。
tā dǎsuàn zhōurì xiàwǔ qù kànwàng nǎinai.
He plans to visit his grandmother on Sunday afternoon.