How much time it takes to experience 4th jhana?

Entering jhana states will be significantly hindered by the will to do so. It is natural process brought on by right efford, right intention and right understanding during the meditation. Achievements in former lives and karma produced in the current plays an important role in whether or not jhana's can be achieved and in which period of time. W. van den Boogaard

There is no short answer to your question. The outcome depends on your dispositions or personality traits.

The sutras explain the difficulties to enter the dhyana realm in terms of five hindrances. The faster you manage to deal with these (very practical!) obstacles, the faster you will progress. Daily meditation time and progress may be correlated, but some people may never overcome a certain hindrance.

A few additional factors may affect your speed of progress:

• Your capacity to concentrate on a single object: Computer programmers or chess players may score higher on this than marketing types :-)
• Your capability to stay awake: Many meditators start to doze away once they manage to lock onto some object and the first cozy feelings start to appear.
• Your curiosity/openness/fearlessness: Every dhyana transition requires entering uncharted territory, which may give rise to different kinds of fears. "Buddhism is not for the faint-hearted."
• Your capability to "let go": You will have to let go the pleaseant feelings of 1st, 2nd and 3rd dhyana in order to advance. You also have to let go of the sense of self and many other features...
• Your "conditions": You won't be able to sit below a tree cross-legged by yourself. Make sure you live in a quite place and act ethically to avoid shame, guilt, remorse and other intensive emotions that will instantly kill your concentration.

And then there is the opinion (couldn't find a reference) that in order to get to the arupa dhyanas you have to get to terms with your impermanent existence, so you would require some progress with the six element meditation or similar insight practices.

If i do meditation everyday for 2 -3 hours, how much time will it take for me to leave the rupa jhana?

It depends on the person. But this this amount of practice I would presume you might not be able to get Jhana. You might perhaps get the 1st Jhana, since based on initial and sustained application to which there is metal activity (active action), but beyond this is will be difficult, as there is not metal activity or there is nothing you are doing (passive / inaction). Even 1st Jhana would be very difficult. Once a monk told me that reaching the 1st Jhana is possible if you practice about 10 to 12 hours a day for about 15 days. And perhaps going beyond this you might have to endure similar practice for years.

• How much time it takes to experience 4th jhana?v
• Right now sometime if i try to concentrate i can feel the calmness in mind. Before 2 years i used to feel inner joy after doing meditation. If i do meditation everyday for 2 -3 hours, how much time will it take for me to leave the rupa jhana?

One cannot put a time perspective on such practices.

Just practice diligently, systematically and with great effort.

Undertake the (samatha) meditation practice for the sake of the practice itself - not for gaining anything. The minute one is thinking about achieving and gaining something, one has fallen into the hindrances.. As a result of that, one has moved away from the primary object of meditation and thus are not cultivating concentration.

Its a good idea to regularly clarify and affirm ones intentions for practicing - especially with Jhana meditation, that is very important. Its easy to become attached to the pleasant sensations this type of meditation practice can result in.

One should ask oneself why one takes on this practice. A wholesome intention is essential. Wholesome intentions for engaging in Samatha meditation could be:

• Collecting the scattered mind (e.g. to be used later for Vipassana meditation)
• Deepening serenity
• Purification of the mind stream
• Cultivating a high level of concentration (e.g. to be used later for Vipassana meditation)

"Suppose a hen has eight, ten, or twelve eggs: If she doesn't cover them rightly, warm them rightly, or incubate them rightly, then even though this wish may occur to her — 'O that my chicks might break through the egg shells with their spiked claws or beaks and hatch out safely!' — still it is not possible that the chicks will break through the egg shells with their spiked claws or beaks and hatch out safely. Why is that? Because the hen has not covered them rightly, warmed them rightly, or incubated them rightly. In the same way, even though this wish may occur to a monk who dwells without devoting himself to development — 'O that my mind might be released from effluents through lack of clinging!' — still his mind is not released from the effluents through lack of clinging. Why is that? From lack of developing, it should be said. Lack of developing what? The four frames of reference, the four right exertions, the four bases of power, the five faculties, the five strengths, the seven factors for Awakening, the noble eightfold path.

http://www.accesstoinsight.org/tipitaka/sn/sn22/sn22.101.than.html