We are in the era of "searchable" documents. An attorney looking for the time of day is not likely to put in "ten" or "four" in his search. The English rules of the 1990s for times don't work anymore. It is correct that English says to put the number into words with the word "o'clock." We have moved beyond that rule.
...He arrived at ten o'clock. (...the way it was done in the last century...)
The rule that ":00" means "o'clock" is just not applicable to the verbatim record and probably isn't a formal rule anyway.
The conclusion: Times on the hour should be expressed with ":00." If you are writing "verbatim," then transcribe the word "o'clock" when it is said.
...He said they would be here at 4:00.
...I know it was getting close to 3:00 A.M.
...She arrived at 11:00 o'clock. (...when the word "o'clock" is said...)
Happy punctuating!
Margie