I rent out my construction equipment on part-time basis. I purchased 1 piece 2 years ago but didn't rent out until year later. What do I put as placed in service date?

I didn't put it in service right away because I wasn't sure I wanted to rent it out.  Putting it in service later actually seems to help me get a larger deduction because the % use is higher and maintenance costs are higher for that period.  The IRS definition seems arbitrary to me.