Hi Arthur,
I'm not quite sure why FormsViewer is showing the time in that format. If you can attach your XSN with some repro steps we can have a look at it, but basically, FormsViewer doesn't really have support for time formatting just yet. We've found that most forms don't make use of time fields (far more forms have date fields, and FormsViewer has better support for date formatting).
If you'd like to show the time in a particular format, I'd suggest creating a separate field to hold the time displayed in the textbox, and use rules to update the actual Time or DateTime field accordingly (using concat(), substring(), etc.).
Please let us know if we can help with that.