Lag time from onset of fermentation

Dumb question ? What does is really mean. Time from pitching to time of the yeast starting to work?

Nothing... I've had beers that didn't bubble, at least not when I was checking them and they've turned out fine. I would tell you to RDWHAHB, but it's 1:30 am now, so probably not a good idea if you have to get up in three hours for work like I do. Hope your beer turns out good. :mug

Thanks for the info. I have seen it on recipes and was curious what is actually meant

It's really the time the yeast takes to reproduce and get the cell count up to where it needs to be for the batch. This is where having properly oxygenated the wort comes into play. More O2 ppms means the yeast has what it needs for healthy/strong cell walls during division.

Post lag is easy to identify too (IME). Most often you can see bubbles forming on the top of the wort (or must) before it kicks into high gear.