+Screencastify announced today in a Google + post that the new update will allow you to create animated gifs.
I spent some time playing with the feature today and it does not look like there is a time limit. You just create an animated gif from any finished screencast. The above GIF, for example, is from a 45 second video.
One neat feature that works very well with the animated gif is cropping. If you were focusing in on the menu you could crop out other parts of your video. As you can see that is exactly what I did in the animated GIF above.
The video below takes you through the steps of using Screencastify to create your own animated GIF.