I did not exactly get your question but if you are wanting to say that what is the duration of any specialisation course after MBBS then for the general MD and Ms courses it is a total of 3 years and you will have to repeat for subsequent years if you do not crack the final examination at one go and continue doing that tell you pass the examination, following which you will have to give voluntary duty at the state super speciality hospitals as a expert doctor in that particular field as per the bond of the state unlike Delhi which presently does not have any such bond
For the perspective of DNB courses most of them are also three year courses but with the more complex serial arrangement and sequential examinations which are to be passed at subsequent atoms and a special mention needs to be made of the six year course where you have a preliminary equivalent master degree and super speciality degree following that and the examinations usually start for DNB Part 1 in such cases from the end of the second year itself and the candidate has to clear them by the fourth year including both the theory and practicals and Oscar tables at external centres which will be allotted as per the curriculum of that particular year and that institution in which they are pursuing the course
after passing the DNB part 1 they will have to appear for the DNB part 2 and pass the examination within a maximum period of 2 years after which if they are still not able to clear both the part 1 and part 2 theory and practical they were have to keep repeating but without employment or stipend
in short it is a 3 to 6 year course which will help you specialise as in case of MD and Ms also the two year DM of MCA course which will be a super specialisation visible acquired through the Neet SS examination will also NTL almost the same number of working as as in case of DNB in case you are unable to clear it in one time
however many experts feel that DNB is ideally suited for private setups and MD and Ms degrees are more apt if you are hunting for government jobs