Understanding Median Frequency Metrics in Mixpanel for Different Timeframes

Hello! When I set frequency metric (example median frequency per user) for last 12 months what is the time frame median frequency is calculated - a month (median of number of events per month per user for last 12 months)? When it's for last 30 days what is the time frame - a day? Or do I have wrong understanding of how frequency is calculated in Mixpanel?