Yes, that is a real bummer with the new weather concept in 3.x. You need to start it when the corn is ripe and you need rain in the evening. So two things must come together and you have only 2 or 3 turns when it needs to happen.
Chance is very slim that this will work, especially since you need to go through this three times. Saving the night before and reloading often would be my best bet.
I hope this will get a re-design, right now this is a horrible quest line.