For those that applied to the USPS, how long until I get my email with the exact first day?

I finally got hired by the company but don’t have a first day exactly. It says anticipated first day. So I’m wary of putting my 2 weeks in in case they push the first day back 1 week or 2 from the anticipated first day. So my question is how long did you have to wait for the email with all the information?
For those that applied to the USPS, how long until I get my email with the exact first day?
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