Nursing for shorter amounts of time after starting solids

My son is 6 months and has been doing great with having solids for dinner every night in between nursing sessions. I've noticed he nurses for less amounts of time and goes a little longer throughout the day. (5-6 mins every 3 or 4 hours) He seems done and satisfied but occasionally my breast is still hard when he gets off so it gets sore until the next feeding. Just worried about that. Is it normal at his age to just need less in general?