The PrecheckReport.Report structure contains estimates of how long it will take an update as well as a list of possible warnings and errors with applying the update.
Time when this precheck report was generated
Rough estimate of time to update vCenter Server in minutes. This field will be unset if the precheck failed.
Lists of the issues and warnings This field will be unset if the precehck is successful.
A summary of the report consist of count of warnings and errors returned by running the precheck.