AM/PM field on zope.schema.Datetime on Plone 4.3

While porting our doctests from Plone 4.2 to Plone 4.3 I saw that zope.schema.Datetime had a new field (AM/PM) that was not there on 4.2.

Is there a way to keep the old behavior (no AM/PM field) as to not have to port all our tests?

If there isn't, examples and tips on how to set them correctly (you don't want to start doing maths in your doctests just to fill an AM/PM field) would be really helpful.