How can compare between times in while loop in sto

Please help me on this, I have been working to do conditions to get the time within the 24 hours only.

So I have something like this. Can anyone help me or tell me if the conditions is correct.

my @DisplayStartTime = 11:00PM

Basically my @nextStartTime = 11:00PM

OPEN cPhosLineTimeSlot

FETCH NEXT FROM cPhosLineTimeSlot
      INTO @Parameter, @DisplayStartTime, @DisplayEndTime, @CodeEndTime, @Frequency, @Tolerance 

WHILE @@FETCH_STATUS = 0
BEGIN
    Declare @nextStartTime nvarchar(30)
    set @nextStartTime = @DisplayStartTime

    --insert into #ActualTimeSlot
    --select @Parameter, @DisplayStartTime, @DisplayEndTime, @CodeEndTime, @Frequency, @Tolerance 

    WHILE (convert(varchar, convert(time, @nextStartTime), 100) < DATEADD(day, -1, GETDATE()))
    BEGIN
        SET @DisplayStartTime = @nextStartTime

        SELECT @nextStartTime = ltrim(right(convert(nvarchar(100), DATEADD(minute, @Frequency, @nextStartTime)), 8))

        INSERT INTO #ActualTimeSlot
            SELECT @Parameter, @DisplayStartTime, 
                   @nextStartTime, @CodeEndTime, @Frequency, @Tolerance 


        SET @intFlag +=1
    END 

    SET @intFlag = 1

    FETCH NEXT FROM cPhosLineTimeSlot
        INTO @Parameter, @DisplayStartTime, @DisplayEndTime, @CodeEndTime, @Frequency, @Tolerance 
END

CLOSE cPhosLineTimeSlot
DEALLOCATE cPhosLineTimeSlot

This is the sample:

If you want to generate all DATETIME values within time period [@StartDate, @EndDate] then you could use a "tally" table:

SET NOCOUNT ON
GO
-- DROP TABLE dbo.Numbers
CREATE TABLE dbo.Numbers (
    Num INT IDENTITY(0,1), 
    CONSTRAINT PK_Numbers_Num PRIMARY KEY (Num)
);
GO
-- It generates all values from 0 to 9999
INSERT dbo.Numbers DEFAULT VALUES 
GO 10000 -- You can insert more numbers if diff. between those two date/time values is greather than 13 days (I used a frecv. of 2 minutes to computes this maximum limit)

and then a simple SELECT statement

DECLARE @StartDate DATETIME2(0), @EndDate DATETIME2(0), @Frequency TINYINT
SELECT  @StartDate = '2015-04-17 11:00:00',
        @EndDate = '2015-04-17 11:15:00',
        @Frequency = 2; -- Minutes

SELECT  n.Num, 
        DATEADD(MINUTE, n.Num*@Frequency, @StartDate) AS RangeStart
        /*,
        CASE 
            WHEN DATEADD(MINUTE, (n.Num + 1)*@Frequency, @StartDate) > @EndDate
            THEN @EndDate
            ELSE DATEADD(MINUTE, (n.Num + 1)*@Frequency, @StartDate)
        END AS RangeEnd
        */
FROM    dbo.Numbers n
WHERE   n.Num <= DATEDIFF(MINUTE, @StartDate, @EndDate) / @Frequency
/*
Num         RangeStart                  RangeEnd
----------- --------------------------- ---------------------------
0           2015-04-17 11:00:00         2015-04-17 11:02:00
1           2015-04-17 11:02:00         2015-04-17 11:04:00
2           2015-04-17 11:04:00         2015-04-17 11:06:00
3           2015-04-17 11:06:00         2015-04-17 11:08:00
4           2015-04-17 11:08:00         2015-04-17 11:10:00
5           2015-04-17 11:10:00         2015-04-17 11:12:00
6           2015-04-17 11:12:00         2015-04-17 11:14:00
7           2015-04-17 11:14:00         2015-04-17 11:15:00
*/