How come my pollen allergies get worse when I get home in the evenings?

Late reaction. Some people with allergies will have a delayed reaction a few hours after exposure, in addition to the immediate reaction.
Delayed reaction. If it is truly a pollen allergy and you have high exposure through the day, you may be experiencing a delayed reaction to the earlier exposure. This often occurs 6-8 hours after allergen exposure and causes similar symptoms as the immediate reaction.