Honestly if everything is okay this would be the worst case scenario:
Best Case scenario:
Case gets delivered to Mike on Feb 27th
Mike assembles and approves the case and ships out to CE/FCC on March 2nd
March 6th - CE testing completed, Test run scheduled
March 13th - Must receive last remaining pieces of mass production
March 16th - Test run of 400 boards
March 20th - Boards arrive for testing
March 24th - Test run burn in completed, remaining run scheduled.
March 25th - Final assembly first 400.
March 30th - first 400 shipped to UK.
March 30th - 2nd 400 start production.
April 6th - Dispatch to customers
April 7th - First pre-order arrives.
April 20th - Final 400 start production.
April 28th - Final 400 clear test, ship to UK.
May 8th - Final 1st batch dispatch to customer.
May 15th - Final pre-order arrives.
This is assuming everything goes to plan, and is based entirely on guesswork and a couple of very long weekends in a factory several years ago
I git to 7th April by coincidence!