As per Higuch-conner method it must me supersaturated solution.

even after phase separation?

Not sure but you may allow the sample to stabilize for some time after shaking. shaking gives external energy ..facilitating solubility.

It is unlikely, unless you heat the solvent for speeding up the trial.

Also, in case the compound contains some amorphous you could experience oversaturation in the initial phase of the experiment.

For both cases, it's a matter of securing to have reached the equilibrium, which has to be defined experimentally, btw.

thank you very much to all

For sure you have to proceed for an efficient phase separation method with a good control of temperature (centrifuge).