This is because the hero leaves ignorant that his wife is pregnant, and returns JUST after she has given birth. (Hey, I can work in the bound of the story I ripped off!)
Complication: this world is realistic enough that seasonal weather patterns will affect travel. He can't overwinter anywhere and burn any of the seven to nine months of his travel time owing to earlier events. So if he leaves in May, he could return in November.
That means that if, on the way out, I indicate time by having the fields full of stubble, it had better be a hay field, not the wheat.