I always thought the cooler growing zones would be easier to set seeds. Early this year when temps and conditions seemed ideal to me, many were difficult. When the temps got warm and even what I thought were less than ideal, everything started setting seeds. So I don't pretend to know the why's, but am not hesitant to try setting seeds anytime. I usually break the pistol back when doing late day or evening crosses to make sure I am not pollinating a dry pistol tip. Also, I am more sure that my pollen and not something from bee's or wind set the seed. If I have something that I find pod difficult and really want to set a pod, I will pollinate a bloom at night which is going to open the next day. This can also be a way to set pods when temps reach triple digits. There are times when the climate just will not allow success around here, like days or weeks with temps over 100. The pods that set will cook off.
Terry