CB Auto Actions acts on triggers. The only way you can schedule something like that is to use the Internal > Users trigger then use CRON to schedule a regular run of the Internal Users URL found within CB Auto Actions > Parameters. Acting on a trigger to do that will not work as nothing is firing that trigger for that user. Your usage of the parse function is also incorrect, see the below example.

Value: [cb:parse function="time"][lastvisitdate][/cb:parse]
Operator: Less Than or Equal To
Value: [cb:parse function="time" time="-3 MONTH"][cb:date format="Y-m-d H:i:s" /][/cb:parse]

You need to contact your host regarding CRON scheduling. You'd need to schedule it to run the Internal Users URL found within CB Auto Actions > Parameters. The action it self just loops every CB user and checks if they haven't logged in within the last 3 months and performs your action. You can also run the Internal Users URL manually.