How long does improving stamina take?

Man, that's too individual. Six rounds shouldn't be a big problem. Be sure you do the necessary for (like running, sparring, rope skipping etc.) the right way, which includes proper resting and recovering. You can try to push yourself a bit (like running the usual distance a bit faster, sparring with "more fire", but I don't mean hurt your partners) and when you manage to improve it, stay on that level for some time until this tempo and effort start to feel not too demanding as they were in the beginning, then try to improve the same way.

I remember there was a period when I was doing fitness, but circuit training for about 30-40 minutes, then I was boxing for about one hour - I think it didn't even take a year to drastically boost my stamina. And no, it isn't wrong doing it, but you know if it applies to your routine.

 

it's not just more running and sparring, it's how you do it. You can run less but with higher intensity or sometimes longer distances at a high pace. You can include hill sprints, swimming and rope skipping, lot of 800m runs with trying to run faster every time. If you rest properly and eat well without alcohol and smoking, results will apply quickly, and even in a few months, you will see a drastic change.

 

Why would you ever want to put a time on it? You improve over time in all areas as long as you train, eat and sleep correctly. Simple as.

 

Have you sparred/fought enough to be relaxed in the ring. You can be an Ultra Marathoner (we had one at the gym, just sparred a few times, was tense and tired quickly) and until you learn to relax in the ring, you won't have boxing stamina. On the other hand, until he moved, we had an ex-boxer who would stop by the gym while drinking. He was over 50, weighed over 220 pounds, couldn't jog 100 yards, had fought at around 125-30, 25-30 years ago and he could do rounds with most of the young fighters. As long as he could fight relaxed he could box all night. If someone made him fight just a little harder than his "pace" he had problems. Anyway, if you're fighting "tense" that could be the problem, if you are already relaxed, just do like viru§™ recommended and keep training.

 

Add to that relaxation and the likes. Fight gasses you way faster when you are tense, mentally taxed and with forcefully irregular breathing pattern.

 

Relaxation, as general and unhelpful it may sound, is the key. It's not so much about breathing properly (exhaling sharpy with punches etc) as it is about not allowing your opponent to keep you in a state of constant fearful anticipation and jerky, uncertain movements. Such cold war wears down a fighter, especially if combined with body punches, even a simple jab to the belly.

 

Remembering to breathe is a good start. It is pretty common for guys, when they get tense and are concentrating real hard, to forget to breathe. It happens when you see a fighter "punch himself out" after hurting an opponent; he got excited and threw a bunch of punches but forgot to breathe.

 

Decent stamina can be build in year or two, first noticible results as fast as 8 week camp

 

If you’ve got a fight coming up then try to do as much sparring as possible. It doesn’t necessarily have to always be hard sparring (in fact, it’s better if it’s not).

The best way to train for a fight is to imitate it and the closest to fighting is sparring. That will defo get you fight fit.

 

I got best conditioning results with Bass Rutten system where you start with 10x1min hard on 1 min rest rounds throwing bombs and you progress to 90s bombs 30 sec rest, And i Tryed it All But the downside is you gotta really whatch out to not get hurt and you gone get hurt probabbly anyway lol also you can't go like that forever you need periods where you take it light witha lot of volume and periods when you throw hard. Another worth mention interval training is 30/30/30 drill great for stamina and pritty safe on your ligaments and bones but That BAss Rutten all out intervals ....Damn crazy fast results but you still gotta have sme conditioning to even start it since throwing bombs for 10 intervals 1 min each is still tough

 

The whole thing is a process and it takes time.
That's why- in the US at least- at certain age groups - you fight 1 minute rounds, then 90 second rounds, 2 minutes, up to 3. And you fight 3 rounds, then you turn pro and 4, then 6, 8, 10, 12. You don't need to have 12 round stamina when you are fighting 3x2. Does that make sense. Guys that are fighting 4 rounds and training for 10 are making a mistake. This is why...
In any fight, and for most fighters, you start the fight with nervous energy which burns off quick. Then you start getting into the fight, you get a little tired and then your conditioning, your 'second' wind, kicks in. You want to train to go hard- to fight your fight- for the number of rounds that you are going to fight. You put it all out in the ring- your second wind does you no good if it kicks in after the fight.
It is your trainer's job to get you to that.
Let me tell you one thing about conditioning and boxing: There is a trade off on what you work on in the gym. You HAVE to master the skills. But it is much easier to get into great shape than it is to learn how to fight- look at Troy Dorsey, and he took some beatings because of it- and the imbalance will always come back to bite you, no matter which side you choose to load up on.