The same as the other time attack achievement for 10 laps.
Choose your class and driver and your track in “Prova a Tempo” under quick modes. If you want to go for a relative short one and a fairly easy track , you should try the Red Bull Ring in Austria or the Sachsenring in Germany. After this start prova a tempo and drive your laps.
It looks like valid laps are not always needed. It unlocked for me after more or less 10 laps and some of them were not valid so this achievement may be al little bugged , but in a positive way for a change.