Hi, we have induced hypertension after a period of 4-6 weeks in S-D rats by administering a 4% NaCl  in drinking water. You should see results in a similar time frame as you are wanting to administer at a higher concentration. did you consider the Dahl strain? 

thanks , can you send me  link of  paper,  who has used this time period , actually i am  using normal sprauge -dawley rats,  not dahl  strain 

2-3 weeks are enough to make them experimentally hypertensive