請看底下link,
http://www.consular.canada.usembassy.gov/nvars.asp
Effective Immediately
All consular posts must electronically confirm all Non-Immigrant Visa petitions petitions prior to visa issuance.
This will affect applicants for H, L, O and P visas. This process may take an additional 2 to 3 workdays, creating a minimum 4 workday turnaround for such applicants. This confirmation is beyond our control and cannot be waived. Any petition-based, otherwise-qualified NIV applicant should be prepared to wait 4 workdays in Canada to receive his or her visaed passport.
We are looking at ways to reduce the expected 4 workday turnaround. U.S. based non-immigrant visa applicants seeking to apply for an NIV are strongly advised to consider applying in their home country.