Dwelling forms include a liberalization clause. it says that any revision of coverage which broadens the insurance without an additional premium charge will be automatically applied to existing policies, if the revision is adopted during the policy period or within:

If it is revised during 60 days prior of the effective date it is ok. This provision is broader when it comes to personal lines than a commercial coverage plan would be. Generally, commercial policies have a time period of 45 days unless the state applies an exception. For dwellings, 60 days would be correct.