Mostly, babies don't need to have their time on the breast 'engineered'....if mum and baby communicate and respond to one another, which is a process that gradually becomes easier over the first days of bf, then all that happens is baby indicates he's had enough on side one, there's a natural gap and a pause, and then another period of alertness and mum offers the other side, which he may or may not take. No probs, no timing, no worrying, baby gets what he wants/needs.
The amount of cream in the milk is directly proportinate to the fullness of the breast. Now, from the baby's end of things, because watery components trickle down to the front of the breast, quite often, he'll get a slug of this when he first comes on . Then, as he continues to feed, the stickier, creamier ingredients come to him with the letdowns.
This has been misinterpreted by some 'well-known babycare authors' as being related to time - you see rubbish advice to 'make sure the baby is on your breast for x minutes or he won't reach the hindmilk' which I can tell you causes a lot of grief and confusion to mothers and babies.
Babies who feed very often come to the breast before the milk has had time to 'separate' in this way, so they will get some of the fattier milk that was 'left' from last time they were on the breast. This is why it is not a 'sin' to let the baby enjoy 'snacking' - this again is something that's confusing,and people think they have to 'make' the baby stay on for longer and to go longer between feeds, so as not to 'snack'.
Yes, one sided feeding can ensure the baby gets more cream in his milk, but as a direct consequence of the lowering of the supply...and this is why one sided feeding is not something everyone should strive for. Many mothers can easily satisfy one baby with one breast all the time, but some can't, and they need to follow their baby's lead in this.
Hope this helps!