The frequency of target settings is almost always unique to every organisation that I have worked for or with.
However, it is a common requirement that clients would like to control access to parts of the process on a periodic basis. In all cases I would recommend using 'Dynamic Cell Access,' or DCA.
You can create a central admin area in the UX which will allow access to be switched on and off across the model. DCA is very specific and allows control at the level of individual line items via a boolean formatted line item sitting in an access control module. How you control this setting however can be designed to fit your desire level of control whether that be the individual, role, department or model wide.