@Shaon-SsS They solved the problem today. Just set the Internet type dynamic IP(DHCP). The time works perfectly now. My IP was static that causes the problem. Thanks to Tp-Link.

@Kevin_Z There is no other router connected instead of WR-845N and C24 on AX20. I check the mail. TP-Link support give me a mail.

@Kevin_Z If I on the DHCP option. then the internet connection will gone. I try this method now and face this problem.

@Kevin_Z Yes you are right both c24 and WR-845N connected with AX20. Both have static IP address. But AX20 have PPPoe internet connection.

@terziyski AP mode not possible. Both router are set on different room. Poor connection not the issue I think. 🤔. Cause my WR-845N also have same time setting problem. Which also set with repeater...

@terziyski