4 mo drinks for 5 min max

I EBF my 4mo daughter. She wants to be fed every 1hr 50min but only feeds for 5 minutes max. Latches and unlatches a lot. Only at times when she's sleepy will she drink for around 8ish minutes that too coz she's sleepy and eventually sleeps. She's fine otherwise but sometimes get cranky when she's sleeping and is rocked to sleep in a swing (flat swinging bed of sorts). At the night we share bed and she's fed while we're both half asleep.

My mil thinks that a baby this small should at least nurse for 30 minutes if she's taking 2 hour gaps. What do you guys thinks?