4 month old nursing

How long does your 4-5 month old nurse on each side? I feel like now that it's the summer unless it's a dream feed or first thing in the morning my daughter only nurses in each side for 6-8 minutes. Is this normal? I know she is a lot more efficient and she still has wet diapers, I'm not worried she isn't eating enough, I just don't want my supply to diminish. Thanks!