time interval in c#

[[NSDate dateWithTimeIntervalSinceReferenceDate:timeInterval] timeIntervalSince1970];

Select  Case 
            When GroupBy = 1 Then 'January - February 2014' 
            When GroupBy = 2 Then 'February - April 2014'
        End As Period,
        Count (Customer_Id) As Total
From
(
    SELECT  Customer_Id,
            Case 
                When Time Between '2014-01-01' And '2014-02-01' Then 1
                When Time Between '2014-02-01' And '2014-04-01' Then 2
                Else -1
            End As GroupBy
    From    db.Table
) D
Where GroupBy <> -1
Group By GroupBy

Select  Count(Customer_Id) 
From    db.Table t1
Where Exists 
(
    Select  Customer_Id
    From    db.Table t2
    Where   t1.customer_id = t2.customer_id
    And     t2.Time Between '2014-02-01' And '2014-04-01'
)
And     t1.Time Between '2014-01-01' And '2014-02-01' 

float tolerance = 0.0001f;

if((CurTime - StartTime) % IntervalMinutes <= tolerance)
{
    // Do something
}

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