You cannot claim beyond the prescribed time limit, ie, which mentioned by CA Akshay Varma.
But may i invite your kind attention to the following;
there is a contradiction between section 16(1) and 16(4) of CGST Act.
and if the credit of march 2020 is something which could be covered in the ITC already claimed in the month of April and May or other months till September then you could say that the ITC of March, 2020 has been already covered and hence the ITC of the Current year ie, 2020-21 can be defer to claim in January GSTR 3B. Above considerations are solely my opinion and you should take due care in accounts and calculations while doing such.
By doing this we are taking our ITC only which were liable to claim and we couldn't claim due to some circumstances.
No Sir you cannot claim ITC of March 2020 ( FY 19-20 ITC ) in your January 2021 month FORM GSTR-3B since the due date of claiming ITC pertaining to FY 2019-20 was 20th October 2020 ( due date of filing FORM GSTR-3B for the month of September 2020 ), which is gone now. So the ITC will be lapsed.