The EGR should not be open during cold start or when the engine is idling, hot or cold. It should only opens during "cruise" operation.
It sounds like the EGR valve is functional, but something is amiss in the control system. I'm not familiar with the specifics of the EGR control system for your model, but if this problem only started when you got the car back from the head rebuild, my first guess would be someone forgot to hook up an electrical connector or vacuum line, or misconnected same.
It's possible that once the EGR situation is corrected the cold start issue may go away.