Scheduled Script Execution ignoring Run as tz settingThe value specified in the "Run as tz" field will apply to the queries where dates and relative date functions are specified when the job runs. If dates and/or relative date functions (such as Yesterday) are used in the job, the values of these dates will be with respect to the chosen timezone.It is not related to the Time specified (the time when the job will execute) for the record.Please find the documentation link for the same - Change a time zone in a scheduled report the job.So, if your requirement is to run the job at a specific time, you will need to manually calculate the time with respect to the System Timezone.