If your lease is silent on the issue, by Colorado statue the landlord has only 30 days to either return the security deposit or to provide a written explanation of why the deposit is being retained. The deposit or statement is to be mailed by the landlord to the tenant's last known address. However, the statue also provides that the landlord and tenant can agree to a longer period, up to 60 days. It is very common for a lease agreement to provide that the landlord has 60 days to return the deposit or provide notice.