A narrow window, not a flexible one
Concrete starts shrinking as soon as it begins to cure, so a saw cut has to go in early, usually within the first day after the pour, before that shrinkage finds its own path. Cut too soon and the blade tears the edge instead of slicing it cleanly, raveling the joint. Cut too late and the slab may have already cracked somewhere else on its own, which defeats the entire point of cutting a line for it to follow. Reading the concrete, not the clock, is what decides the moment.
Saw cut or tooled, and why it is not the same cut
A saw cut is one way to put a joint into a slab. A tooled joint is the other, made earlier, while the concrete is still soft, by dragging a hand groover across the surface instead of running a blade through firmer concrete later. Both end up doing the same work, giving the shrinkage crack a line to follow, but they happen at different points in the pour and they look a little different once the slab has cured. Which one a job gets usually comes down to the finish and the schedule, not a rule that applies everywhere.
Where the cuts get planned, not just measured
Saw cuts do not go in on a fixed grid regardless of what sits on the slab. On a floor that will carry equipment, an anchor bolt set too close to a saw cut has nothing to hold onto if the concrete around it lets go, so the cut pattern gets drawn around where equipment will sit instead of straight through it. On a driveway or a patio, the layout follows the shape, the thickness and where the slab meets a garage apron or a step. Either way, the cuts get planned before the saw ever touches the slab.