Depends... are you going to add a CUC all at once? Once your tank cycles, I would give it a week to be sure there are not any fluctuations. Once this is done, I would add a few hermits, snails etc. to your tank. In another week I think you could then start adding a hardy fish and more CUC.
I don't recommend those "all in one" CUC's at once. Although, I have done that before in the past.