Flangelina - it sounds to me you don't trust the process yet. You are constantly worrying if the current feed is long enough, or if the previous one was maybe not long enough...and also worrying about the overall total of his intake.
It will help to trust breastfeeding, and your baby. It's absolutely the case that babies of this age take what they need in a very short time.
There is nothing wrong with 'snacking' - I really don't know why this is supposed to be a terrible thing with babies. It means feeding for a short time, fairly frequently, which is a perfectly ok way for a human being to behave, and we all do it. With a baby of 5 mths, they do not whither away if they don't get the opportunity to feed little and often on some occasions, of course, so they can be left for short times with someone else, or if it is not convenient to feed, something else can distract them for a little while.
In a month or so, your baby can have other foods and drinks, too.
To be honest, accepting it and going with the flow, is likely to be easier than trying to change things, when they are going to change anyway with weaning.
Bf is clearly working well for you and your baby - analysing it and timing it and wondering if something is enough....well, it doesn;t help, IMO!