The incremental С2С backup of SharePoint site finishes with warning:

Failed to process change event Item/Add.

You have created a backup plan of Office 365 data to be performed by a cloud agent (cloud-to-cloud backup).

You notice that backup is in the 'backing up' status for many hours.

Comparison of Office 365 protection options in on-premises deployment and Cloud deployment of Acronis Cyber Backup 12.5. To learn more about on-premises and cloud deployment see product documentation.

(!) The table describes features available in Update 3 (Build 11010) and later. Some features are unavailable in earlier builds.

You have Acronis cloud agent for Office 365 and create a backup plan. You cannot find where to specify backup start time.