(These are the guidelines that were suggested during the FAA rebate program back in 2019. 15-20 minute flights are usually plenty for getting valid ADS-B data)
To summarize the requirements of AC20-165B (see links below): The performance flight should take place for a minimum of 30 minutes from wheels up. The aircraft should climb to 3,000’+ AGL and perform a minimum of 2 360 degree turns in each direction. Banks in excess of 30 degrees and extreme maneuvers and attitudes should be avoided. Any climb or descent should be a minimum of 1 minute in length. The area of flight should have excellent radar and ADS-B coverage. A map of the current ADS-B coverage at various altitudes AGL is located here: https://www.faa.gov/nextgen/programs/adsb/ICM/
Operational Flight Evaluation. Conduct an operational flight evaluation (OFE) per section 91.407(b) and request an FAA ADS-B compliance report.
Reports are available from https://adsbperformance.faa.gov/PAPRRequest.aspx
Flight profile guidance is provided in section 4.3.2 of AC 20-165B: https://www.faa.gov/documentLibrary/media/Advisory_Circular/AC_20-165B.pdf