It’s not really about duration so much as frequency. You’re trying to recognise their sleep/wake pattern. So if you know they’re always active (regardless of how rough or for how long) for 7 different periods a day and then suddenly this drops significantly that would be reduced movement. If you google count the kicks there’s some really insightful stuff on there and you can get kick counter wristbands to track movement and learn how much is normal.
My midwife told me that every baby is different and there’s a pattern that forms and it’s different for each baby. Mine moves basically all the time, so If he hasn’t moved in two hours I’d call the triage line because I know what’s normal for my baby and what isn’t. I think as the pregnancy progresses and they get bigger and run out of space the way you feel them is different - which is why you probably feel stronger movements. I’m sure everything’s fine, but if you need reassurance definitely go get checked or ask your midwife about it. My midwife said to me “I’d rather have you come everyday for reassurance than miss something because you don’t want to bother me”
My baby only tends to move if I’m relaxing on the sofa or in bed. When I’m active he doesn’t move as much. So I do understand the confusion xxx
I’m the same it feels more like a Mexican wave now rather than little kicks. There running out of room so probably harder to move.