You have Acronis cloud agent for Office 365 and create a backup plan. You cannot find where to specify backup start time.
Office 365 backups with Acronis cloud agent run once a day. As this type of backup requires Acronis cloud resources, which are shared among all clients, workload on these resources is spread in time to ensure stable performance.
Save your backup plan. It will run automatically once a day.
You can run it manually by clicking Run now.
If Office 365 backup runs at inconvenient time, you can revoke and reapply the backup plan from the backup console and backup time will be randomly changed.