As long as your not putting too much tension on the connective tissue your not over stretching. Don't listen to possum. Your muscle are not like play dough. Your muscles aren't what make you flexible. muscles only stretch so far then the connective tissue takes the remaining stress.

Yes you can only do splits by stretching the groups for that particular movement or position.

Here is an. Article I wrote on the science of stretching

http://burrovago.com/?p=331

You're stretching too much. You need at least a day's rest in between your workouts.

If you are young - someone who has not gone through final growth spurt - you can get away with doing a middle split by practicing little else than a middle split. This will take a long time and will frustrate your progress. And you will injure yourself in the end.

If you do it the proper way, then you should be doing at least mild weightlifting, warmups, and isometric exercising.

Your muscles can be visualized like playdough. Ever take a wad and roll it into a snake? What happens when the snake gets longer and longer? The snake body gets thinner and thinner, and becomes weak. That is what your muscles do when you do nothing but stretch. To solve the playdough problem, you add more playdough as you lengthen the snake. To add muscle mass, you need to do mild weightlifting. Otherwise, what little muscle fibers are there will be responsible for all of the strength and stability in your legs.

Ever see someone throw and hold a side kick? The kick, and as they try to hold, their foot/leg drops a few inches. That's because they have the flexibility to get their foot at that height, but they don't have the strength to keep it there. That means, at that range of motion, their kicks are not controlled. In a case of kicking without muscles to control, you can injure someone if you can't control that kick, or you will strain a muscle if you can't control it. And, of course, you don't have strength - so there is loss of speed, balance, control, and technique.

I think it would be better to devote 1 hour every other day to your stretching.

I agree with possum that rest in between is needed too and the longer time will allow you time to also warm up properly before stretching. You will get much better results in stretching when warm.

So warm up first. Jog, jump rope, bike.

Hold each stretch for 2 minutes or more.

Relax your muscles. Tight muscles don't stretch. Relaxed muscles will give you less resistance so make sure you don't tighten up when it starts hurting.

Breathe. Breathe out when going into the stretch, hold the position when breathing in, lower again on your breath out. Keep your breathing even and normal. Huffing and puffing will make you tighten up, which will hurt more,...

Avoid injury. Pulling or even tearing something are set backs as your tears heal thicker to prevent re-injury.

Be patient. The success is not in the quantity of your stretching but much more in the quality.

Go to youube and type in 'flexy Friday' the people that run the channel are very flexible and know what they are doing. They have a few videos on how to achieve middle splits

I want to achieve the middle splits but I'm just wondering if I can achieve it by only doing the middle splits stretch?

I stretch for 20 minutes 2 - 3 times a day.

So my question is: Can the middle splits be achieved by only performing the middle splits stretch and nothing else.