20 - 40 minutes
My Mac mini was making noise for like a month after that it started turning off after every 15 minutes. After this i took my Mac mini apart and realize that fan was the problem it wasn't working. I almost went to buy the new Mac when my friend tell a bout Ifixit. So I check the site out and after looking at few guides order a new fan and fixed my Mac.
Repair was smooth with no problem thanks to guides.
Before you start throwing out you Mac or Idevice check with Ifixit. And save some $$$