One other thing to think about is what exactly constitutes a 'reasonable amount of time'? I've heard multiple stories of het to het breedings that took three or more clutches before finally proving out. Sure, statistics say that one out of four eggs from a het to het breeding should give you a visual, but anyone who has actually bred more than a few clutches knows that it doesn't always work out that way.
Heck, I've only been breeding for a few years and I've hit some pretty bad odds in that short amount of time.