When you exit your long/buy option positions or enter new write/short options, the proceeds or credit of option premium can be used for only new long/buy option trades on the same trading day and only within the same segment (proceeds from equity options can’t be used for any other segment or vice versa).

You can use this proceeds or option credit for all other types of trades only from the next trading day.

Let's understand this with an example

You have sold Options and received a premium of Rs 1 lakh. Derivative trades ae settled on T+1 day. This means that the payout from exchange for your options premium is only on T+1 day. Now if we allow you to take a position with this premium in any other segment on the same day, then while reporting margins to the exchange we would have to report short margins in your account as the premium received is not yet realized and cannot be reported as per statutory guidelines. So your account will get charged margin penalty by the regulator. To avoid this penalty levy we restrict the use of premium received to trade in any other segment on T day.