I have searched for a correct place to post this with no results. I did not want to highjack the thread of someone else. So here I am with my question. Using Time Machine has not been something I participated in pryer to deciding to upgrade to El Capitan. After reading all the advise about having a secure backup before attempitng an upgrade of a new OS I decided to activate my option for TM (time machine) using and external drive. I am not pleased with the options for TM backup which lists backups as often as every hour. Ones a day or even less would be find for my not so important computer use. Sorry for all the writing to approach my situation. QUESTION is, if I leave the external driver that TM uses turned off during the day or even a few days. How will the backups be done when I do turn on the external hard drive? Thanks for your advise in this not so important matter.