"In Use" date for tax deductions - furniture

[AJ D.]

I understand the IRS views the first day of your rental to be when it's available for use (not when you purchase) but how does this impact business/tax deductions?
For example - I have a rental property that is put in-use on July 1st, but I bought furniture throughout the months of May and June. Is this furniture able to fall under the de minimus safe harbor even though it was purchased before the officail "in-use" date? If not, how do rental property owners tend to deduct furniture and other appliances that are purchased before the formal in-use date?