format time

I would use a formula to convert the times.

Try this:
J2 =TIME(LEFT(B2,2),MID(B2,3,2),RIGHT(B2,2))
or this:
=--TEXT(B2,"00\:00\:00")

You should also convert column A to actual dates.
To do this, highlight column A > Data > Text to Columns > Next > Next > Date: DMY > Finish

In another column on your sheet, enter the following formula
=LEFT(B2,2)&":"&MID(B2,3,2)&":"&RIGHT(B2,2)

Now Format column B as HH:MM:SS
Copy the data from your new column, and Paste Values back to column B
They will now be stored as true times which you can prove by entering in another cell =B2+1/24 and you will get a time wch is 1 hour greater 17:10:36

You can't make time entries to a cell as 161036, you have to enter as 16:10:36

Just in case it's relevant: none of this is going to resolve the mismatch issue I flagged in your commercial services thread earlier.