Tatkal is opened on the basis of departure from the Originating station.
Thus while from the stations it departs on the very same day, it opens 2 days in advance, for the stations it departs on the 2nd day, the ARP would count to 3 days and subsequently 4, 5 or 6 days even.
Thus, one needs to take in to account the nature of Tatkal booking of a particular train during a particular time or a particular week day.
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the trains which have a nature of getting full on the opening day, one has to waste money and book it from the stations falling on the first day of originating.
Smartness to this extent can be applied that we book from the station which falls last on the origination day.
The Boarding point can later be changed in case of E tickets while for Counter tickets, it can be changed at the booking time only (first the clerk will issue the ticket from the originating day station and than will change).
There are some trains which have different quota from some stations (I am not very sure) and if one wants to avail it from such stations, he can wait for.