Pre-orders and previews begin April 10, launches April 24.
Apple's Mac Pro Shipping Estimates Move to March in Many Countries
The change in shipping estimates does not necessarily reflect a worsening supply situation given that estimates have been listed at "February" essentially since launch last month, but they do indicate that Apple is not making up significant ground as lead times appear to be remaining in the six-week range.
The new March shipping estimates are in effect for stock and build-to-order configurations throughout Apple's online stores for Europe, Middle East, and Africa (EMEA) and Asia Pacific (APAC) operational regions. Estimates in Apple's stores for the Americas remain at February for the time being.
Update: As of January 21, Mac Pro shipping estimates in the United States, Mexico, and Canada have also slipped to March.