If your GTDt order validity date falls on a non trading day, then ASL will consider the valid date prior to such order validity date.

For example:

You have placed a GTDt request first on July 27, 2015 for buying 100 shares of Reliance at a Limit price of Rs.900 with order validity date of 24-10-2015. In this case:

Start Date = July 27, 2015 Monday

Validity Date = Oct 24, 2015 Saturday i.e. Trading Holiday

Thereby, if on July 27, 2015 your Cash order with GTDt order validity date of Oct 24, 2015 remains unexecuted or partly executed, then ASL will consider the validity date prior to such order validity date (Oct 24, 2015) and if order remains unexecuted then this order would be Expired.