Try for at least 24 hours but for as long as 48 hours. Another tip: use less starter. It's counterintuitive, but using less starter usually means your bulk fermentation will be longer, which means your starter will go through its food source at a slower rate and therefore produce more acetic acid along the way.
When you handle the dough after its bulk fermentation, it will feel quite different to when you first handled it. The dough will now be very light and have a 'bouncy' kind of a feel to it. In fact, if you give the bowl/container some gentle movement backwards and forwards, the dough will 'jiggle' and be wobbly.