当天 + Time/Event
当天 (dāngtiān) means "that day" or "the same day" and is used to refer to a specific day already established in context. It functions as a time word and is typically placed at the beginning of a sentence or before the verb. For example, 当天下午 means "that afternoon."
我们到达北京,当天就去了长城。
Wǒmen dàodá Běijīng, dàngtiān jiù qù le Chángchéng.
We arrived in Beijing and went to the Great Wall that very day.
当天晚上他就给我打了电话。
Dàngtiān wǎnshang tā jiù gěi wǒ dǎ le diànhuà.
He called me that very evening.
合同签好后,当天下午货就发出了。
Hétong qiān hǎo hòu, dàngtiān xiàwǔ huò jiù fāchū le.
After the contract was signed, the goods were shipped out that afternoon.