Itc related

Last date of September 2020 month GSTR 3B return or annual return date. Which ever is earlier .

Due date of Sep return for succeeding year or date of filling of annual return whichever is earlier

Time limit to claim ITC against an Tax Invoice or Debit Note is earlier of below dates:

The due date of filing GST Return for September of next Financial year (i.e 20th October)
OR
Date of filing the Annual Returns relevant for that Financial year.

So, as per above it's 20th October, 2020 for F.Y 2019-20