Check the following link about the definition "Placed in Service" for depreciation eligibility.
http://www.irs.gov/publications/p527/ch02.html#en_US_2010_publink1000219035
according to this definition, you can defer the depreciation until your property is fully ready for rent. for example, you bought a property in Nov 2012 and it took 2 months to renovate. you started advertising in jan 2013. this is so called "placed in service". you can start depreciation in 2013.
