Time scale in pivot chart

I have done a pivot chart where the X axis shows time values in
HH:MM:SS format. Or it SHOULD, but instead displays in date log
format.

So, instead of 7:53:21, it will show 0.331 or something.

How can I change the format of the axis display?

Mmm, think I found it. The help file mentions that time formats for
pivot chart axes are taken from regional settings - whatever is
selected on that PC for Short Time, Medium Time etc.

I'm using a custom time format. Seems that nobody up in the MS clouds
coded for this type of contingency - date format in table does not
match one of those in the regional settings, so, she go foof! Boring.

Has anyone found a workaround or have different thoughts on the problem?

Thinking a little more, the reason I use a custom format is so I can
use it to display periods of time. It shows how long a task took,
separate to when it started or stopped. The best solution I've found
is to use a time field, with no AM/PM displayed.

Are there better ways/data formats to deal with variables/fields that
store periods of time, not clock times.