That's an interesting question. My best guess is that the hidden fields will not be evaluated, but I suggest making a duplicate of your layout and using it to test the concept to see if this is really the case. Then let me know if my educated guess is correct.
Your mention of a calendar brings to mind this recent demo file that I concocted for iOS devices using FM GO. It's a portable calendar format date picker that can be swiped horizontally to move from month to month within the date picker: https://dl.dropboxusercontent.com/u/78737945/DatePickerPopoverDemo.fmp12
I doubt that it is something that you'd want to use here, but you may find it a useful source of ideas.
Thanks so much, Phil. This knowledge base article hasn't been updated since FileMaker 12, but I'm hoping that this behavior holds true with FileMaker 13's new "hide object when" functionality: http://help.filemaker.com/app/answers/detail/a_id/10235/kw/hidden%20fields
Thanks for the calendar demo, too! I will check it out on FM Go!! :)