At how many citations should I make my Google Scholar profile public?
As someone who is currently on a search committee for two tenure track positions in mathematics, I can tell you that "hiding" your profile certainly won't help.  In the job search process, potential employers are going to want to know about your research and its impact.  It's common to check on Google Scholar, Math Reviews, Web of Science, and similar databases to see what impact a candidate's research has had.  Many of the candidates for faculty positions that I've seen don't have public profiles, and in my opinion this makes them look weak in comparison with candidates who do.

If you don't have a public profile then someone trying to evaluate your research who looks at Google Scholar will probably find one or two of your most cited papers or perhaps find nothing and assume that you have essentially no citations.  Another possibility is that they'll find a confusing bunch of papers written by other authors whose names are similar to yours.  Having a public profile ensures that they'll see all of your publications and citations.  Even if there aren't many citations yet, this also shows that you're aware of the importance of documenting your research activity and its impact.