Longer running jobs are not formally supported right now. Currently though a project will go to sleep when the user stops interacting with it at 15 minutes (if the rsession is idle) or 24 hours (of the rsession is busy).
In theory that means that if you run code in a cloud project and come back within 24 hours the code should still be running. Also you should note that there's 1GB memory limit right now in cloud so running this on a larger data set might present some additional challenges.
Sean