Timestamp for received ADS-B Information

I’m currently on a project involving the display of air traffic information around multiple operating UAS in rural environment. The received information from multiple receivers needs to be merged together to complement the whole air traffic image.

For this I need accurate time information about when the ADS-B message was transmitted by an aircraft in order to compare how up-to-date each received information form a UAS is. As far as I know there is no timestamp transmitted with ADS-B by the transponder of a vehicle.

Is there an option for me to detect when a UAS received a specific ADS-B message? The only option I am aware of is using the timestamp of the ADSB_VEHICLE MAVLink message which won’t be as accurate as I am aiming for.