With SetCronJob, you can set up cronjobs to run at random time, e.g. every hour, at random minute; or every day, at 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.
You can also select a specific time range you'd like your cronjob to run at, e.g. every day, at a random hour from 9AM to 5 PM: just select all values between 9 and 17 (select 9, scroll down, hold Ctrl and select 17, it'll select everything in between).
When the cronjob is created/update, click Logs > Scheduled executions to see when your cronjob will be executed.