Would like to have "Length" of track in html report

I'm trying to get the "Length", time, in the html report of my mp3s. The HTML_Standard does have the column heading "Length" but does not report it I'm guessing that the string I have in there is incorrect to report the "Length" but I have no clue as to how to change it. The string that I have in the body of the report is:
<td$if($odd(%_counter%), class="odd",)>$replace(%length%,&,&).

I know this must be wrong because the "Length" has to do with time and it's probably not reported as text, so my question is how do I change the string to report correctly?

It is %_length%, not %length%.

Thanks. I do not know coding soooooo.......

Don't worry, finding that subtle difference isn't obvious anywhere (and even in the dialogs inside of MP3Tag, it does not suggest that string, only the one without the underscore (i.e: %length%).

This is true if you have used a user-defined field with the name %length%.
To test this, you could reset the list of fields to its original contents with the functions in the right-arrow-menu next to the list.
Otherwise you find the reference to %_length% in the help on exports:
http://help.mp3tag.de/options_export.html#placeholder
and also in the list of information fields - not in the list of tag fields.