In my experience a crack of any length = window replacement.
Also, if electrical arcing is observed within the window.
We do measure and monitor delamination according to limits defined by the manufacturer and/or type certificate holder. The limits depend upon type and manufacturer. In general, arcing occurs once delamination reaches the bus bars and a window should be replaced before any delamination reaches a bus bar. Thus the rate at which delamination is occurring is the limiting factor. Obviously any delamination in the direct line of vision would also be a good reason for replacement, but delamination generally occurs at the edges and progresses inwards.