My reference is live unamplified music so no matter how often I make changes my reference stays the same.
I try to keep a component at least four to six months. Many components can take up to 600 hours to break in and settle. (ie: Audio Research SD 135 Stereo Amplifier)
After break-in I usually will take another three or four weeks to put it through its paces with various types of music and power cord trials.
A few times I have been undecided and had components waiting in the que to be added to the system. If it is a deal and the price is right I may take a flier on a piece that I anticipate working well for me. I can worry about selling the loser later.
I once had four SACD players and three pair of speakers at the same time. Rare for me! Everything I was looking for came on the used market at the same time!