Wow! That is a really fast growth to look fine in the morning and be molded that evening. From what I read mold only germinates in 6-12 hours and can take 1-12 days to actually colonize so for you to have something molded over in a matter of hours is baffling! First, are you 100% certain it's mold? I know that sounds like a stupid question but like I said given what I read it's like supernatural for something to grow mold that fast so I was just wondering if it might be something else? (I have no idea what else it might be...I'm just throwing out possibilities here. lol) I would def try the gfse before tossing as from I've read it is a pretty potent antibacterial/antifungal and in theory should take care of any active mold/mildew. After that I would try relocating my diaper pail to the coolest, driest enviroment possible since mold needs a warm and wet enviroment to thrive. I wouldn't think that having dried them outside would have increased mold growth so long as it was sunny that day and they dried thoroughly. Do you have a mold problem in general? I know some areas are more prevalent than others when it comes to mold growth. I don't really have any other suggestions...perhaps someone who has actually dealt with it more may be more helpful. Good luck!

How long did it take your diapers to dry outside? I know mine are often not 100% dry after 5 hours of being outside if it is really humid. Also, I've found I have to hang them and not lay them flat.
Hope this helps.