DECLARE @start [datetime] = 2010/4/1;
Should be...
DECLARE @start [datetime] = '2010-04-01';
The one you have is dividing 2010 by 4, then by 1, then converting to a date. Which is the 57.5th day from 1900-01-01.
Try SELECT @start
after your initialisation to check if this is correct.