The period of limitation shall be-
six months, if the offence is punishable with fine only;
one year, if the offence is punishable with imprisonment for a term not exceeding one year;
three years, if the offence is punishable with imprisonment for a term exceeding one year but not exceeding three years.
But this is only when the cognizance itself is not taken:
Except as otherwise provided elsewhere in this Code, no Court, shall take cognizance of an offence after the expiry of the period of limitation.
In your case the FIR and charge sheet were already filed duly very long back hence this section may not be applicable to your case.