GST related query

As per rule 37(2) of gst act itc reversal if the payment is not within the 180 days
Please clarify me in the following doubt
1.payment means only for GST portion or whole amount in sundry creditors (ie, taxable value+GST)?
2. Instead of payment cash discount is received from debtor in that case 180 days payment rule is applicable?
3.while reclaim of such itc reversal, time limit of claiming itc (September return due date or actual date of filing the annual return which ever is lower?) Is applicable on such itc?