Nclex for indian nurses

hi everyone,
i m an indian registered nurse, want to write nclex-rn. but want to go to utah and write examination,
can any one tell me how much time it takes to get credential evaluation for indian nurse and ATT. and should i start process before going to USA OR after reaching there. actually i m planning to come there on study visa so tat i ll be having time to clear exam in two years. so even i ll come there on atudy visa , retrogation process will affect me ?
pls reply me soon if any one is having information. thanks in advance.