How long before you pivot? - successful founders only

As a distinctly unsuccessful founder (lots of side projects, very little revenue / traction to show for it), I'm curious for folks that have successfully founded businesses with traction:

How long do you advise people stick out an idea with low traction? How much pivoting off the original idea is acceptable?

If you're also a nights / weekends founder, would love to connect :) either at @ laplacemonk on Twitter, or irl if you're also based in nyc.