Earlier self install date

Most cases you can. If you have already received your equipment of course you can plug it in, make sure to accept terms and conditions on att.net/uverse.

Can you plug your equipment and connect the service wire, yes…

will it work, most likely not if the outside work and provisioning have not been completed.

Which internet speed ordered?

For copper based self installation service, connections are generally made the day of expected service between 8 am and 8 pm. This can include to the port at the Central Office (CO), remote terminal (RT), or VRAD. The tech should also check service at the NID if accessible then closes the job. If do not have service within 24 hours after schedule need to call in as issue might be the wiring from the NID to the expected wall jack. 

For fiber service self install, tech might still need to make connection at the PFP for the assigned splitter.