Thanks, bertie.
I think you have explained it well.
Of themselves 40 mins plus feeds are not a concern. In fact, it's wholly impractical to have this as a benchmark. Babies tend to stop and start during a feed. They might take a few mins rest. They might be sucking vigorously and then rest a bit, but staying on. How can anyone possibly get an accurate picture of the time the baby is actually feeding? Stop watch?
In addition, sometimes babies do not have 'feeds' as separate entities. They have sort of 'sessions' :) where you are not sure if they coming to the end of one 'episode' or beginning another one.
But let's say you somehow time your feed by the clock, and calculate if you are on the sofa for forty mins plus there's something wrong. My point is there might not be - is the baby happy, thriving, growing, nappies normal, mother comfortable? If the answer is 'yes' then we may have a conversation about why this is not a sign that things need changing.
However, other children, busy life, mother literally unable to move from sofa all day every day, mother overwhelmed.....then we might explore ways the mother can spot when the baby is finishing, other ways to offer comfort, ways others can help.
It's individual. But to pathologise feeds of forty mins plus, and/or to train peer supporters and health visitors and anyone else into intervening or offering intervention, is to undermine confidence in what may well be a perfectly happy, rewarding breastfeeding relationship.
Being dogmatic about the time a 'feed' ought to last is how we get into a right mess.
Babies are individual, as are mothers, as are situations. Certain principles apply, nevertheless, and one of those is that you cannot, must not, assess breastfeeding by the clock.