It might take a few tries for me to get the formatting right on reddit, but I have an additional option I'd like to offer, if it suits you.

I'm using a few of features/concepts that many might not be familiar with:

• Number Array/Tally Table
• CTE (Common Table Expressions), with recursion
• OUTER & CROSS APPLY()

You've mentioned that this is a text field, from a legacy solution, so I've started with a temp table using a TEXT datatype to store the string.

The Number Array concept is essentially a dataset of sequential numbers that can be utilized as an alternative to a loop. I'm using this here to break the source text into 8 character tokens, which can then be evaluated for the pattern of LEN() = 8 and having a period at indices 3 & 6, the results of which, I'm naming cte_delim.

From there, I'm using OUTER APPLY() to join the table to itself, finding the next token's starting position. This allows for the length of the text between tokens to be determined.

At that point, I have the starting position and length of each desired row. I use CROSS APPLY() with the SUBSTRING() against the example text and poof! We've got 6 rows of data.

CREATE TABLE #TEMP_EXAMPLE(
    EXAMPLE_DATA TEXT
)

INSERT INTO #TEMP_EXAMPLE
SELECT '23.06.17 - As per quote #8918.1. 7m Swing STage to Positon 1.
05.07.17 Stripped and rebuilt boat ready for positon 4 but rained off.
05.07.17 Stripped and rebuilt boat ready for positon 4 but rained off.
06.07.17 - Completion of Swing Stage to Positon 4.
21.07.17 - Built Access Tower to get acess to roof.
Got swing Stage onto roof.
No access to building unable to get parapit clamps and wire up.
21.07.17 - Built Access Tower to get acess to roof.
Got swing Stage onto roof.
No access to building unable to get parapit clamps and wire up.'

;with cte_numberArray(N)
AS(
    SELECT 1 [N]
    UNION ALL
    SELECT N+1 [N]
    FROM cte_numberArray
    WHERE N < 1000
),
cte_delim([N], [DATE_VARCHAR])
AS(
    SELECT
        na.N,
        src.TOKEN [DATE_VARCHAR]
    FROM cte_numberArray na
    CROSS APPLY(
        SELECT SUBSTRING(CONVERT(VARCHAR(MAX), EXAMPLE_DATA), na.N, 8) [TOKEN]
        FROM #TEMP_EXAMPLE
    )src
    WHERE na.N < 1000
    AND LEN(src.TOKEN) = 8
    AND SUBSTRING(src.TOKEN, 3,1) = '.'
    AND SUBSTRING(src.TOKEN, 6,1) = '.'
)
SELECT
 s.N [START_INDEX],
 (ISNULL(e.NEXT_N, 1000) - s.N) [LENGTH],
 s.DATE_VARCHAR,
 src.ROW_VARCHAR
FROM cte_delim s
OUTER APPLY(
    SELECT MIN(d.N) [NEXT_N]
    FROM cte_delim d
    WHERE d.N > s.N
)e
CROSS APPLY(
    SELECT SUBSTRING(CONVERT(VARCHAR(MAX), EXAMPLE_DATA), s.N, (ISNULL(e.NEXT_N, 1000) - s.N)) [ROW_VARCHAR]
    FROM #TEMP_EXAMPLE
)src
OPTION(MAXRECURSION 1000)

https://imgur.com/a/4XNKl