Snapshot

I have installed snapshot & linked it with dropbox - however I cannot seem to change the backup interval? I did an immediate back-up from first use locally - before changing the options to dropbox, I don;t know if this has conflicted anything?
I have made a backup to dropbox but this again was using the immediate set up. Would like to have the option to get this weekly - Any help would be appreciated -
P.s - I'm a newbie to wordpress :disappointed: