We all know that there is time and life in pop

However, there is no control field about time in Pyro

If I want to control a smoke, it is clear at the beginning and fuzzy after

Is it impossible to control, only through speed control

But this is not what I want. I want to control based on time

Excuse me, is there any solution? Either I don't see this control field, or I need to create one myself. Is there any case or tutorial?

Do you mean how fast the smoke/density fades away? You can control this through the "Dissipation"-setting.

Hope that helps.

Particles are points with a clear emitter, trajectory and lifespan. In pyro, you can't track from which specific source smoke density in a voxel might come from. So what you're looking for will be most often achieved by using other control fields in the forces of your pyro sim, namely temperature, density and velocity, which tend to be higher near the source of your sim and gradually go down.

Age or life doesn't exist in Pyro, as there is no way to define any kind of id/smokeParticle or whatever to track smoke.
Voxels are just stationary and contain float or vector values which - god knows how - get advected and (partially)carried over to the next voxel each Frame depending on velocities/forces/etc.
Atleast that's my understanding of the matter.