eh if it's just out of a pipe I don't usually hold it in longer than 3 seconds or so. If it's good shit out of like a bong or something I'll hold it in a bit longer.

Sometimes if I only have enough for one small bowl (basically one hit) i'll hold it in longer just to maximize the effect of what little I have.

Sometimes I put resin on top of the bowl to make it last longer but it makes the smoke a bit nasty, so I only hold it in maybe 1-2 seconds.