The length of time it takes UPS to ship the package after the label is created depends on when the package gets to UPS or when UPS picks up the package.
When a seller prints the label for UPS it means that the seller has packaged the item and printed a label and paid for the shipping through UPS.
Some small sellers may take the UPS package to UPS and some small sellers may have UPS pick up the package.
It can take a few hours to a day before UPS gets the package in it's possession.
Large Companies have UPS pick up the packages at their business or even have a separate company deliver the packages to UPS.
But once the label is created for UPS your package should be in UPS possession within a few hours to a day.
Then it usually takes a few days to get the package once it's being shipped within UPS network.