If you drop premium channels, how soon can you add the free promo?

[whatchel1]

Right now have HBO & SHO. If I drop them how long would I have to wait to get the free promo for 3 months.

 

[KAB]

Right now have HBO & SHO. If I drop them how long would I have to wait to get the free promo for 3 months.

I had to wait a year from the time the promo started.