It should take you about an hour to learn how to draw basic pixel art. Then after that, you decide yourself how much time you want to spend each piece. The more time you spend nitpicking, the better it'll look. And of course it's gonna look better with experience, as practice makes perfect. But it's one of the easiest things in the world to learn, tbh. I honestly don't like it much, yet even I'm able to draw some kickass 16- and 32-pixel sprites. Go online, on youtube, whatever. And download GIMP or Paint.NET for free (I use the latter, but many prefer GIMP over Paint.NET, as well).
And yes, you should definitely learn how to draw some basic pixel art, if only for the making of crude textures that helps convey your game to a potential publisher or whatever. But you don't technically need to learn it. Using the internet effectively, you can get resources for free, and even hire people to do stuff.
But sitting down for a day or two and browsing the various articles and youtube, in order to get the fundamentals down? Not exactly a titanic investment, if you ask me.