Check pay delays in mailing - being mailed later than requested/expected

It appears that there is a several day lag between when Quicken says that a check will be issued/mailed by the Check Pay system and when the check actually is postmarked and deposited into the mail.

I Entered a check payment for immediate release on a Sunday. expected that the check would be mailed Monday.  When the check was received, the payee told me that the check was mailed from Denver and the postmark was on Wednesday.  I'm trying to figure out why it would take so long to print and mail the check.