Method of putting boric acid into nickel sulphamate bath

While using nickel sulphamate bath, whether boric acid, which acts as a buffer, should be dissolved in the solution or should it be kept in pp bag dipped inside solution, whats the reason for the same, because according to my observation when dissolved inside bath, after the solution cools the boric acid precipitates down in the beaker and moreover it takes lot of time for initially dissolving the boric acid.

Your observations are absolutely correct. Since you say that you are using a beaker, you can add the required boric directly to the solution. Remember that the boric sample needs to be from the nickel solution when it is at temperature. The boric does not enter into the reaction. The loss of boric is mainly from drag out of the solution.