Jumping rope -- How long can you go?

It depends on how fast you go. I change the speed a lot when I jump rope so it's not too boring. I take approximately 2 breaks of a few minutes per half our of jumping, but it doesn't really matter if you take breaks as long as they're not too long and your heart rate doesn't go down.
It's also a matter of technique, if you jump really high and swing your arms wildly it's much more fatiguing.

longest i've gone was 25min. It's fun for about 2-3 minutes then it gets old.

I started being able to do 1-3 minutes.  Which was about 20 jumps before I collaspe in a panting heap.  And my coordination was so off I could only do 2 to 3 revolutions.

I'm now up to 45-60 minutes per day every day...  My routine is do 40 jumps then I walk around for 10 -20 seconds between sets to relax the calves and shins.  I do not count a set that I trip up with a count less then 30 revs, nor do I walk around after the trip up unless I am super tired.  I force myself to do a clean 30 rev minimum but aim for 40.  I do roughly 40-50 sets depending on my energy level and coordination.

I found that I increase my coordination weekly and then jumping is with the ball of your feet pushing and the movement is in your ankle.  Anything is is more difficult and requires more energy.

I also found using a weighted rope (2.5 lbs to 5 lbs) helped me as I found I could slow the rope down and still keep a good pace.  A cheap cloth rope or a speed rope requires the rope to spin to fast for me.

Once I've done about hour with breaks like 2 minutes etc...but than I wasn't able to run or go up/down stairs for one week...than i was doing jump rope for 20 minutes....the key is to change styles (i mean to switch left right or jump backwards or do 10 left 10 right than 10 "normal" etc. -with this it won't get boring that fast...) and also stretching calves is important-before,after and during!!...try to write jumprope cardio routine into the youtube and you can choose the one which fits your level...

i find this exercise quite exhausting....my heart rate speeds up and my calves are not so happy ;-)  i should try this more often....

Ok, here goes the real deal.
Since im a former thai boxer, and this sport requires a huge amount of rope jumping, i can tell you this.
Rope jumping is all about technique people. Believe it.
You can easily learn how to rope jump by doing 1 single rope jump at a time, then try fives and so on.
The trick to this is to buy a rope that is not really big and also not really light.Those plastic cables are not good for you, as they are way too light and need shoulder movement to keep the rope cycling around you.
Go barefoot for starters. I know what u think, barefoot? me? no way! Actually rope jumping barefoot is easier as you can mentally calculate the jumps and the distance between your foot and the rope. When u can do it ok, wear your shoes and u will notice that u will trip it almost every 5 jumps. Remember to NOT use a metalic cable rope when goind barefoot, if you trip it, your will painfully skyrocket into your ceiling and your toe will have a new purple cool look.
Right rope size is: Take a rope, hold it properly with your hands being little bit above your waist (10cm above your pants belt). Ok, step on it with both legs, leave 30cm space between your feet. Thats is about the right size for you.
Keep your hands CLOSE to your body.
Use your wrists to cycle the rope with high momentum, do not expect the rope to cycle itself. Also do not move your hands too much, just cycle your wrists and move your arms to increase speed or correct the rope.
Do not jump too high, 10 cm from the ground is still high.
Do not bend your knees too much, u are not doing squats here.
Do not go very slow, this is hard even for pro jumpers. Going fast is easier for your legs and will increase your cardio limit really fast.
Do not jump stationary like a pillar, u will look ridiculous and yet tire your legs out. Dance it up, change your leg position a bit with every jump.
Do not do double jumps or triple jumps, u are not Rocky. Those are high stamina exercises, not cardio and will dry your muscles away.
Make sure your hands are closer to your body when u jump and focus on your arms, not your legs for the jump, arm movement is 90% people.
Also do not, yes, do NOT have both of your legs jump at the same time, you will tire yourself faster. One leg goes front the other goes back. Jump with your rear leg, use the front one only for balance, merely touching the floor.
Ok you say, but jumping with one leg with hurt your leg, true, when u feel your leg cant take it, switch legs in the following jump and continue. Alternate legs like that. 
Do NOT use your entire foot surface, jump only on your front part of your feet. Using your hole foot is hard and will hurt your anckles.
You will see that after a day or two, u can do 40s or 50s with no trips. After a month u will be able to rope jump for 15 minutes with no breaks or trips at all.
I can rope jump for ah hour like that, no kidding. When i stopped boxing i could rope jump for 90 minutes. 
Just remember that it may seem hard, but so far i cant find anything better for cardio. Rope jumping is easy, doesnt need that much room, no need to buy expensive rope (find a plain 1cm diameter rope and cut it to your size), and is killer for warming up your ENTIRE body.

Thats all, feel free to judge me.

I'll have to try that.  I do the jump one foot then the other foot maybe this would be, for me, 10 rev on one foot 10 rev on the other.  Qorse case it allows to switch it up.