How much time do we need to notify an employee of his start time being pushed back 2-4 hours ? There is a weekly schedule posted w/ changes from week to week. But if there is no work for them at there schedule start time the next day we push it back anywhere from 2-4 hours. We do let them know the night before. Are we breaking any state laws ?

What you are really asking is whether IL has a report pay law (i.e. employees must be notified by X amount of time prior to their shift if work is not available or employees are entitled to a certain number of hours of pay.) A search of IL's DOL website did not suggest they have such a law but you can take a look around if you like: http://www.state.il.us/agency/idol/index.htm (look under FAQ's for IL's wage and hour laws) or you can give them a call to be certain.

As far as I know, California is the only State with a report pay law.

Massachusetts and New Hampshire also have reporting pay laws but as far as I know those three are it.