The documentation doesn't say much other than
starttime datetime The time the package began to run.
Does this log as UTC ?
It appears you are using SSISDB, not msdb. The table you reference (msdb.dbo.sysssislog`) is used by one of the (old) package deployment methods for SSIS, not the new project deployment method of SSISDB.
The logs stored by SSISDB are access by browsing to the package in the Integration Services Catalogs node in the Object Explorer of SSMS; navigate to the project and package, right click it and select Reports and then the one you want.
All the times displayed in the SSISDB logs are accurate to the second, and are displayed in the server's local time.