Itc on capital goods under gst

Dea All, 

           We are registered as first stage dealer under excise and also whole sale trader, we want to buy a capital good (Machine) from inter state of RS. 35 Lacs + excise duty+ 2 % cst ...my question is that when it should be purchased i.e. now or after implementation of GST so that we can take input tax credit on capital goods immediately? thanks in advance