Husband and the birds & bees...

So my husband thinks I'm crazy that there is only a small window of time to ttc. He thinks it can happen anytime and to fret for a week is completely goofy... I've shown him charts, I've gotten books on it, and even other couples have told him and yet he still thinks it's complete bs... I'm not sure what to do to get him to understand and to help me out during that time.... any ideas?