You can, but your app will be running in the 'free app' mode just like the sandbox. and thus shuts down automatically after a while (2 hours if i remember correctly).
This also limits your use of scheduled events etc.
To add to what Larn said, you will also be limited to creating 5 accounts for this app.
If your app were to go to sleep you would need to navigate back to it in a browser to wake it up.