feeding and cow's milk?

My son (he'll be 1 next week) normally nurses 4 times per day. For the past few weeks the amount of time that he nurses during 2 of his feedings has REALLY decreased. I have not yet intriduced cow's milk and won't really be able to for another week...we're going out of town for the week and he's had bad reactions to a couple of foods, so any new food is introduced very slowly and I don't want a sick baby when we are away from home. So, is there any type of urgency for me to strat giving him cow's milk since his nursing has decreased or do I follow his lead on this? He eats a well balanced diet of solids and drinks water with them.