Premium Credit to Account

When does the premium is actually credited to the seller’s account? Is it only at the time of expiration? What happens if the sell CE/PE position is squared off before expiration?

You receive the premium when you take Short Position. You can check this under Option Premium column on Kite funds page.

The difference between the price at which you took short position at and the price at which you square-off your position at will be your P&L.