What does pdamp and tdamp mean exactly?

Consider this code:

units real
fix 1 all npt temp 500.0 300.0 100.0 iso 50.0 10.0 100.0
timestep 2.0
run 2000000

In this code, will pressurure and temperature be relaxed in the first 100 femto sectonds and then run for the next ~4 ns at the final temp and pressure? Or is the change gradual throught the entire run time?

Thanks!