DECLARE @table1 TABLE (
    time time,
    button char(3)
    )

insert into @table1
select '9:00','Off' union all
select '10:00','On' union all
select '11:00','On' union all
select '12:00','On' union all
select '13:00','Off' union all
select '14:00','On' union all
select '15:00','On'
SELECT * FROM @table1

;WITH 
buttons_all AS (
    SELECT
        time, button, ROW_NUMBER() OVER(ORDER BY time) AS row_num
    FROM @table1 ons
), 
buttons_first_ons AS (
    SELECT
        time, row_num
    FROM buttons_all b_ons
    WHERE        
        button = 'on' AND
        EXISTS(SELECT 1 FROM buttons_all b_all WHERE b_all.row_num = b_ons.row_num - 1 AND b_all.button = 'off')
),
buttons_first_offs AS (
    SELECT
        time, row_num
    FROM buttons_all b_offs
    WHERE        
        button = 'off' AND
        EXISTS(SELECT 1 FROM buttons_all b_all WHERE b_all.row_num = b_offs.row_num - 1 AND b_all.button = 'on')
)
SELECT 
    b_ons.time AS [On],
    ISNULL(b_offs.time, (SELECT MAX(time) FROM buttons_all)) AS [Off]
FROM buttons_first_ons b_ons
LEFT OUTER JOIN buttons_first_offs b_offs ON
    b_offs.row_num = (SELECT MIN(row_num) FROM buttons_first_offs b_offs2 WHERE b_offs2.row_num > b_ons.row_num)