With FastCron, you can set up cronjobs to run at a random time, e.g. every hour, at a random minute; or every day, at a random time (hour and minute).
To do so, when editing/adding cronjob, select desired time interval at When to call .e.g. Every hour, then click Exact time, check the Random box at Minute and/or Hour field, and Save changes.
When the cronjob is created/updated, click Logs > Scheduled executions to see when your cronjob will be executed.