I was looking for the same type of backup too (Backuping automatically a number of session/tabs/windows at an interval).
I also use Freshstart but it no longer work.
To be safe I always use 2-3 extension to automatically save my session at each 5-6 minutes.
Here's one that work flawlessly since many years:
https://chrome.google.com/webstore/detail/tabs-backup-restore/dehocbglhkaogiljpihicakmlockmlgd?Another one but since the last version (6.0) it's not reliable anymore since the extension crash and stop saving session:
https://chrome.google.com/webstore/detail/tab-session-manager/iaiomicjabeggjcfkbimgmglanimpnaeWhat is also important for me is to be able to export/import those sessions so if the extension crash I can recover. Another feature that I would like is an automatic upload/sync each day on my Google drive/Dropbox of my session, so if my whole computer crash I can recover.
Also for privacy reason I prefer to save my session to my own cloud (MY dropbox or My Gdrive) instead of a third party.
Best Regards !