hi,

iit and nits have btech admission process from the first year of b.tech studies, students who have passed 12th or appearing in 12th exam may apply for jee main, however jee main exam can be attempt by 3 consecutive years starting from the year of 12th passing. see diploma admission can be done after 10th also, students who have studies diploma after 10th dont have good knowledge on mathematics which is taught in 10+2 course, and iits or nits curriculum is comparatively standard to other state government colleges, so that may be the reason that they have no entry scheme for diploma pass candidates.