Work permit approval

Hi all.

Recently, I received an approval letter from the IRCC for my open work permit. I was provided with a document number, expiration date, and travel document number.

My question here for anyone that knows, is how long do I need to wait to work or can I work right away? Will I receive a document in the mail saying that I can work with a different number?

Any help in this area is much appreciated. Thank you.