@ Author (mr. M. Munikrishnan)
1. As per S. 167 (2) CrPC of CrPC the time limit is prescribed for filing the charge sheet are as follows;
1.1 Ninety-days, where the investigation relates to an offense punishable with death, imprisonment for life or imprisonment or imprisonment for a term of not less than ten years.
1.2 Sixty days, where the investigation relates to any other offense
Therefore in your case the time limit is SIXTY DAYS if there is only S. 420 mentioned (where the imprisonment in this section is maximum for 7 years and fine).
2. However in case of continuing offence there is no time limitation as the continuing offence give fresh cause of action for taking the cognizance and then there refer to the section S. 468 and S. 472 CrPC.
BTW, is my guess that only S. 420 there correct for this brief purpose as I intentionally ignored other IPC sections which to my guess may not have passed test at cognizance stage ?