I've messed up my Mavericks mini & I need to nuke the hard drive & start over. I don't have an external drive to use with Time Machine. I know that I can use an external hard drive. According to the Wikipedia article on Time Machine, TM will do a full restore of the OS. My question is, can I set a restore point in TM before I make a change & then roll the OS back if I mess up? I can use a 3rd party application like Acronis True Image as well.