Congratulations!
Immediately once you have a CSCE (Certificate of Successful Completion of Examination), but you must identify differently on the air until your upgrade is live in the FCC database. If you just upgraded to General exam, you will add /AG to your call sign. If you just upgraded to Amateur Extra, you will add /AE to your call sign. (Usually said as "yourcallsign, temporary AG", or "yourcallsign, temporary AE"). If you are one of the rare operators upgrading to a Technician license from a Novice, you would add the suffix /KT at the end of your call sign. ("yourcallsign, temporary KT").
Once the license upgrade is reflected in the FCC database, you may use your call sign as you normally would. W4VEC prides itself on filing fast and efficiently. If you pass the exam during the week, the database is usually updated within 1 business day (often in only a few hours). If you pass the exam over the weekend, the update will usually happen the first business day after you pass the exam.