The Opportunity Stage Duration report is a standard report that shows how long opportunities spend in each stage before they are closed. It can be used to measure the average stage duration for all closed opportunities by grouping and summarizing the data by stage name and duration fields. Using process builder to capture the daily average on each opportunity is not feasible because it would require creating multiple fields and formulas on the opportunity object and updating them every day. Adding formula fields to track stages on each opportunity is also not practical because it would require creating multiple fields and formulas on the opportunity object and maintaining them every time a stage changes. Refreshing weekly reporting snapshots for closed opportunities is not necessary because the report can run on real-time data without snapshots.
References:https://help.salesforce.com/s/articleView?id=sf.reports_opportunity_stage_duration_report.
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