Tires Rotating in Opp. Direction

[PotenzaSub]

My older brother needed to use my car for a hiking trip he went on today. So, last night (actually this morning at 6) I had to change the summer tires to the winter tires b/c he is going to be driving on dirt roads.

Anyway, I hadn't gotten any sleep all night (b/c I had to work out abd by the time I finished it was like 3 and I decided it would be easier to just stay awake then have to get up with only 4 hours of sleep) and I was pretty incoherent.

After figuring out how to jack up the car, I had to rush to change the tires b/c I only had about 30 minutes to change the tires and check the air pressure. I put the tires on, checked the air, put air in, and rushed to my brother's apartment in NYC. I drove slightly agressively since I was late.

Anyway, i got there and parked. I walked around the car and to my amazement both rear tires were put on backwards (wrong rotation). In my sleepy state I must have forgotten to check that they were put on properly. The front wheels were OK though.

So, my question: how bad is this situation? The car is 2000 subaru RS 2.5 (AWD obviously). And i think my brother will be driving all the way to Maine for his trip.