What to know about the national emergency test on Oct. 4 : NPR
The test is scheduled to begin at about 2:20 p.m. ET on Wednesday, Oct. 4.

The testing window runs for 30 minutes, but you should only receive the message once.
https://www.npr.org/2023/10/03/1202900361/a-nationwide-emergency-alert-test-is-coming-to-your-phone-on-wednesday#:~:text=When%20is%20the%20test%20happening,scheduled%20for%20the%20following%20week.