Ok, I updated the tool. Now it backups the database immediately if an internet connection is established.
@TechniSol: you can check yourself the cpu usage
Just ssh your Kobo and do:
On my device, when it doesn't backup the db, cpu usage is 0.4% at max. he tool reaches this cpu usage only every 3 seconds.
I can't find a way to detect sleeping status, but I suppose it doesn't really matter: db can't change while Kobo is sleeping, so the auto-backup tool remains at that level of cpu usage.