This app was only made to restore single files. I didn't find the feature request (not sure if there is any) to add a function to restore all files of a folder to be before a given date (if you don't find it either, make a new feature request on github.com/owncloud/core/issues).
So for your case it would probably be faster to make a full restore of a backup (if you have).
Regarding the file-locking issues, have a look at the FAQ: https://central.owncloud.org/t/file-is-locked-how-to-unlock/985
Also the current version of owncloud is 8.2.9. But before you run updates or do anything else, backup all you have in the current status. There are background processes running all the time and you want to avoid that they delete some old versions by accident.