I've always heard that after 7 seconds your lungs have already absorbed all the usefull cannabinoids it can from the hit. When I was younger I used to try to hold it longer and can't recall it ever making me feel higher.
If you're trying to conserve try cutting back, do small bong hits and force yourself to wait a few minutes in-between. Most people try to rush the process of getting high, much like some people rush trying to get drunk faster by consuming their alcohol quickly. In either case it's possible to consume more then is needed to achieve a satisfying buzz and in the process we waste some by consuming too much in one sitting. If we slow the process down we often find that a smaller amount is plenty for us to get high off of. We might even find it more desirable because we didn't end up taking too much and thereby had more control of ourselves.
If you're trying to conserve try cutting back, do small bong hits and force yourself to wait a few minutes in-between. Most people try to rush the process of getting high, much like some people rush trying to get drunk faster by consuming their alcohol quickly. In either case it's possible to consume more then is needed to achieve a satisfying buzz and in the process we waste some by consuming too much in one sitting. If we slow the process down we often find that a smaller amount is plenty for us to get high off of. We might even find it more desirable because we didn't end up taking too much and thereby had more control of ourselves.