Unfortunately there is a lot of misinformation, misunderstanding, incomplete information etc out there. I would recommend following a source of good info like an IBCLC or your local La Leche League group perhaps or joining one of the BF support groups on FB etc. Or even a good book? Amy Brown and Lucy Ruddle are some BF authors I like. Lucy Ruddle has just brought out a great book correcting loads of popular myths! I will also link some helpful videos, blog posts etc at the end of this post.
You don't need to "drain" a breast, this is a myth anyway as breasts are not like bottles which need to be filled up and emptied. Milk is basically being made all of the time but very slowly (imagine a dripping tap), it will "pool" in your milk ducts between feeds, particularly in the early days which is why your breasts will physically feel full. They are, but it's not because they're holding the entire volume of your baby's next feed, it's just a kind of overflow holder. When your baby latches on and begins to suck you'll get the letdown reflex, which tells your glands to produce faster (imagine the tap being turned on) - this is the bulk of your baby's feed and it's being produced as they drink it. As they get full, the speed and strength of their sucking will reduce until they are just doing that fluttery kind of sleep sucking and may fall asleep, unlatch or fall off the breast as they lose the tension in their mouth. Once they have slowed down sucking, you'll be back to the dripping tap kind of production, which (hopefully!) means you won't squirt milk everywhere when they come off. (This happens later when they are an easily distracted 3-4 month old and your toddler does something very interesting across the room! They unlatch in the "tap turned on" phase and you leak everywhere.) But anyway, because they reduce the flow by themselves when they've had enough, you don't need to worry about whether things are "draining" or not because that's not really how it works. Some women can always continue to express milk after a feed and some can't, no correlation to supply BTW, so feeding until empty is not a useful goal and nor is it a necessary one.
By the same token, keep baby on one side until they come off by themselves or they get agitated/fussy on one side and then swap over. There are situations where you would ignore this and swap them more regularly or put them back on the same side, but these are for specific situations - for most people, don't count minutes at all (if you're using an app, put it away because they encourage you to uselessly count minutes - this will cause confusion and stress) just watch the baby and swap when they seem to be finished. They might or might not want the second side. Again, trust your baby. If they want more, they will let you know.
Some babies are fast feeders and some are more leisurely feeders. Many have varied length feeds. Some people count only the fast, strong sucking as the feed time and take them off (or stop counting) when they get to the fluttery bit and some let them stay attached and may even count this time as the feed continuing, so might be counting a lot of time when the baby is actually asleep and milk is only slowly dribbling in. Sometimes during cluster feeding in particular, they will have one of these strong sucking sessions, then doze off and do a bit of fluttery sucking or just stay attached and then wake up and do a bit more strong drinking triggering another letdown, so it can even be hard to tell when one feed has ended and the next one has started, which again plays havoc with the counting of minutes, and probably accounts for some of the wide variation that you will come across when talking to other breastfeeding mums. BTW, it is beneficial to let them continue when they are doing the fluttery sucking, so if you don't want/need to take them off, then it's fine (and helpful!) to let them continue. But it's not totally necessary to do it every time, so if you do need to go somewhere and want to put them in the car seat, or really need a wee and want to put them down or just are fed up and want a break, it's fine to break the latch once they change to that. But they are getting milk when they do it, they are not "just using you as a dummy" (as some people will tell you).
Totally agree that their poo often has very little correlation to anything, it will vary, it's almost always just poo.
Here are some links which might be helpful :)
www.analyticalarmadillo.co.uk/2010/07/foremilkhindmilk-and-lot-of-confusion.html
This was a great one but is now gone! I have found it on web archive which means it takes longer to load - it's not broken if you're getting a long wait time.
web.archive.org/web/20210617162525/thefunnyshapedwoman.blogspot.com/2011/05/foremilk-and-hindmilk-in-quest-of.html
The other BF videos on this channel are great too.