No written response to requested assignment

[LadyK]

Due to many difficulties with our apartment, we have requested to assign our lease. The management company has said that this is fine and to go ahead and find someone, however the actual landlady is a real old dragon (that's putting it nicely) who has a phobia about putting things in writing. I'm aware that if they say 'no' to assignment without reason then we can give them 30 days notice. We've sent a letter by certified mail requesting this and are yet to receive a response, how long should we leave it before giving them the 30 days notice. Aslo,is not giving us a written response at all the same as saying no?