The date format can be edited directly in the My Account Payments Component or My Account Transactions Component templates.
For this, the following code:
HTML
<div class="expiration-date">\n {{event.date | date:'MMM d, y h:mm a'}}\n</div>
can be updated to:
HTML
<div class="expiration-date">\n {{event.date | date:'MMM d, y H:mm'}}\n</div>
This will show the time and date in a 24-hour format without AM or PM references.
A list of attributes that can be used in the time formats is available here.