I would imagine it would not be too long. I would say a few days maximum. If they are still being shy, you can do a few things:
1) move the whole tank around
2) try adding a couple new neons to the mix
They should be out and about in no time I would think. Once they learn that the bully is gone, they usually go back to being comfortable. As a side note, I have found that sometimes a bully will often cause them to stick together. Do not be suprised if they stop schooling once the the threat is gone.
What did you end up doing with your Gourami? Sometimes you can take them back for trade? Maybe try a different store?