Guivenancio, I do believe that it does take longer with shaders. And you can pause a Render, But! You can`t close Minecraft and continue the next day... I Think.
Or what you can possibly do is, Save the KeyFrames and continue the do the Rendering when you can.
Here is a video of CrushPixel Demonstrating it. Enjoy! :D
Other than that, You should try to update everything and try Restarting your computer. If you havent already! ;)
Is it Really Slow When you render? Example: 15-second video, takes 30 mins to render...