You can run daily trunk utilization reports in the CDR analysis and reporting module in CUCM. You can get to it through servicability.
Once you have CDR reporting up, click on Device Reports / Route Plan / Route and Line Group Utilization. Select the route patterns that correspond with your PRIs and run a report for a single day, then look for the busy hour. This will give you your highest utilization rate for the day. Do not be tempted to run a report for a longer timeframe that one day. If you do, you will get average utilization for the timeframe.
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