I have previously written about landlords that find themselves on the receiving end of litigation because they fail to return the tenant's security deposit (or provide a list of damages) within thirty days of the tenant leaving the property.
The statute provides that a landlord must return the deposit or provide the damage list within thirty days of the "termination of a lease or upon surrender and acceptance of the leasehold premises, whichever first occurs . . . " or the landlord is responsible for double the deposit. 68 P.S. 250.512(a) and (c).
Landlords often say that the tenant did not return the keys and they are not sure when the tenant actually left (thus beginning the thirty (30) day countdown). Don't let your dispute turn on when the tenant actually surrendered the premises. In most court disputes as to when the tenant actually left, the tenant will win. Tenants will lie about when they left and the courts will often believe them. Send the letter as soon as you think the tenant might have left. Don't wait for the thirtieth day. Don't get hung up on whether you received "official" notice or the keys. Courts don't get hung up on those issues. Neither should you.