25 hours a day?...
25 hours a day?
It all depends on what you're trying to do / learn. For example, as GoinEasy9 says, you can become a proficient end user in a couple of days, if you already have end user experience with another OS. On the other hand, it could take you longer to learn how to become a proficient sysadmin, or a network application developer, or maybe even a kernel developer.
Like anything else, the more you put into it, the more you'll get out of it.