Split time in intervals of 15
Hello I create a temporary table variable type to not create the table

DECLARE @tbl_provider_available_schedule TABLE
    (
    [id] [int] NOT NULL IDENTITY(1, 1),
    [practiceid] [int] NULL,
    [providerid] [int] NULL,
    [providerlocationid] [int] NULL,
    [fromDate] [datetime] NULL,
    [toDate] [datetime] NULL,
    [appointMode] [int] NULL
    );
    INSERT INTO @tbl_provider_available_schedule
    (
        practiceid,
        providerid,
        providerlocationid,
        fromDate,
        toDate,
        appointMode
    )
    VALUES
    (1, 1, 2, N'2019-09-19T11:00:00', N'2019-09-19T11:45:00', 0),
    (1, 1, 2, N'2019-09-19T11:00:00', N'2019-09-19T12:00:00', 2),
    (1, 1, 2, N'2019-09-19T11:30:00', N'2019-09-19T11:45:00', 1);


    WITH CTE
    AS (SELECT fromDate AS [Time],
               1 AS RLevel,
               id,
               toDate,
               CASE appointMode
                   WHEN 0 THEN
                       'office'
                   WHEN 1 THEN
                       'home'
                   ELSE
                       'tele'
               END AS mode
        FROM @tbl_provider_available_schedule
        UNION ALL
        SELECT DATEADD(MINUTE, 15, [Time]),
               RLevel + 1,
               id,
               toDate,
               CTE.mode
        FROM CTE
        WHERE DATEADD(MINUTE, 15, [Time]) &lt;toDate--We tell you not to miss the end date
        )
    SELECT id,
           [Time] AS StartDate,
           DATEADD(MINUTE, 15, [Time])  as EndDate,--add 15 minutes more
    CASE WHEN mode='office' THEN 1 ELSE 0 END AS Office,
    CASE WHEN mode='tele' THEN 1 ELSE 0 END AS tele,
    CASE WHEN mode='home' THEN 1 ELSE 0 END AS home
    FROM CTE
    ORDER BY id;


analyze it and you commit me.

PD:The final result is different because in your insert there is more data, notice that by the ID it looks like it was.

Demostration:

https://dbfiddle.uk/?rdbms=sqlserver_2017&amp;fiddle=b02953ffbc0d70fe1e863a43e63c551f