The charting time of this train from DLI is 12:00 hrs sharp. Since this train, especially its 2S segement constitutes of a major chunk of last minute planners, most of the travelers plan to book on the same day in the morning. But since IRCTC is not the best of the sites to be at from 08:00 hrs to 12:00 hrs, from practical observation I've seen many ending up NOT being able to book because by the time they impress her highness, Miss IRCTC, men at DLI are done with their paperwork.
it is advised to book before you sleep the last night. Or at most book in the morning by 8. Don't rely on current booking. The queues at DLI are horrifying and so is the traffic on the roads!