The EOs take 30 days. Same as rejoining the Paris Accord.

"In one of his first acts in the Oval Office, President Joe Biden signed an executive order to have the United States rejoin the Paris climate...
..It will take 30 days for the U.S. to officially rejoin the agreement, but meeting its targets is going to be a taller order. The U.S. is the second-largest producer of carbon emissions, behind China, and has contributed more to global climate change over time than any other country."

https://www.npr.org/sections/inauguration-day-live-updates