In the case of e.g. cereal crops in the north, there are 4-6 months where you can do little beyond some maintenance, buying/selling equipment, planning next year's crop, etc. that means there is plenty of time for vacations. You are right that during seeding or harvest (especially), all bets for travel are off.
But, it is incorrect to imply that because you farm, you ought to kiss vacations good-bye.