Is there an IDE or SDK that could be likened to developing for Android? I mean, if it looks like creating stuff using NetBeans or something similar. I've never even got my hands on anything running Android yet, so go easy on me.
I'd also like to ask if, given that you already have all 2D graphics ready, how much time would it take to make a small (1 stage) platformer or top-down perspective game? A day or two perhaps?
You generally develop for Android with your favorite Java IDE (Eclipse, Netbeans, Intelij Idea). The officially supported IDE is Eclipse. In addition to your standard Java development setup (IDE + JDK) you have to install the free Android SDK. Programming for Android is pretty much the same as programming any other Java application: create a project with the correct type in your IDE, write Java code against the APIs provided on Android and run/debug your app either on the emulator or a device connected via USB. A good starting point is the Android Developer Guide.
Graphics alone don't make a game, a common misconception. In general you have
With experience (emphasis on experience here) one can create a VERY simple platformer game in a day. I did that for the last Ludum Dare, a game development challenge where you have to write a game in 48 hours. You can find out more about it here (with source code).
Here's a timelapse of the complete 13 hour creation period.
Pulling this off needs a lot of experience though, something that takes a while to acquire. I can not claim that you can do the same in the time frame i used after reading the book, but you should be able to do it in a few weeks if you don't have any previous game development experience. Can't really generalize here, it all depends on the individual and dedication.
The Android SDK provides the tools and application necessary to begin developing applications on the Android platform. In which the graphics design on the game program, Depend the syntax approval and guiding on them. An android is supporting to the Java script.