Quashing

Quashing of the FIR is a discretionary power of the HC and depends upon whether the contents of the FIR prima facie point towards a charge against the accused. The HC doesn't embark on a voyage to determine the sufficiency or lack of it of the evidence of the prosecution. Quashing is limited to making an inquiry as to whether the FIR prima facie discloses a charge against the accused, or it has been registered with an oblique motive to harass him. Quashing happens rarely, much less the quashing of the chargesheet. Consider moving the HC before the filing of the chargesheet if you can prove that the FIR is false and the proceedings are an abuse of the process of law.

Quash happens on legal grounds only.  If u have one, move ahead to HC, its right time dear

It makes no difference whether you file it now or afterwards.  However if you file it now there is a possibility that HC may postpone its decision till police submit its report to magistrate because there is a possibility that the evidence that has not been there during FIR stage may be gathered by police through proper investigation.  So without knowing the result of investigation, the HC may not arrive at conclusion about quashing the proceedings.  However, if the FIR is too frivolous and ostensibly smacks of intent about malicious prosecution, the HC may quash proceedings now itself.