Upgrading applications built on frameworks like Laravel or Rails.

Quick question for my developer savvy friends. Been learning Laravel and Rails side by side, compare and contrast almost. I am more familiar with PHP, and thus Laravel is naturally more fluent to me, but Rails has me in a honeymoon phase with how intelligent it is.

With that said, I know that Rails goes through regular updates, and I know that for instance the lessons on Laravel here are on V4, but currently Laravel is on V5, and there were some fairly significant differences that I had to figure out on my own compared to the videos.

I know the answer to this question must be a fairly practical answer, but for either framework or both, how important is it to update your application after the a new version of the framework comes out? Can you not do the update until you want a feature that is part of the newest update? And when you do start the update, is it something that can usually be completed in a few hours, or even a few days? Basic re-factoring of the code to ensure you're following the newest version's conventions?

And finally, I imagine that ensuring you stay up to date enough that the framework is current with the language it is using (PHP or Ruby) and that version of the language is supported by your host, is an important reason to stay current, but how fast does this process move along?

Thank you to all that help me understand this part of the process.