"Break-delay-make" relay?
If you need a delay between break and make that is anything more than in the millisecond range then your best bet is to use two separate relays for this application. You can integrate a simple electronic control circuit between the input control signal and the two relay coils to take care of the delay characteristics that you would need. The following simple circuit implements a break-delay-make for both transitions of the input control signal. 





You would wire to the individual relay contacts to achieve the type of switching that you need for your application.