23 February 2018
Once you entered you Input Tax Credit it will appear in the Input Ledger automatically, so that you can use them for setoff of your credit anytime. however their is a restriction only for taking an fresh input credit on old bill which is 1year after filing your annual returns
26 February 2018
There is no restriction in law for carrying forward ITC credit. The restriction is only for claiming credit which has to be claimed before filing Annual return or September. Eg: for the period 2017-18, credit to be claimed before filing an Annual return or Septemeber 2018 whichever is earlier.