You can’t specify a date with ‘Good Till Cancel’. It just means that the order will remain valid until either it is filled or it is cancelled (for example via CancelOrder): so it will persist beyond the end of the day’s trading session, whereas a ‘DAY’ order is only valid till the end of the session.
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Don’t confuse ‘Good Till Cancel’ with ‘Good Till Date’ and ‘Good After Time’, where you can specify a date and time.
I was going through TWS API order structure. I found that we have GTC orders in which we can specify date and time to cancel the order. Why we have seperate field called autoCancelDate? Isn't it same as GTC.