In the Funnels report, if you use the line chart visualization with a daily time interval, Mixpanel runs a separate funnel for each day in your date range. This means a user can enter and be counted on multiple days. [Funnels FAQ]
Measurement to use: Set the measurement to Unique Users (with the Uniques counting method) and select the final step (or "All Steps") to measure conversions. [Counting Methods]
This gives you a daily view of unique users who converted, where each day's funnel is independent.