RailFans - we wander, but never get lost - Shaurya Kumar

Tatkal Rules:
Tamilnadu Express Train No.2622
Train departs : from New Delhi 2230 hrs on 28 10 2010
Departs: from Nagpur 1430 hrs on 29 10 2010...
more...

I wish to have tatkal e-ticket
The software allows tatkal booking two days in advance excluding date of journey
As such I can book tatkal e-ticket on 26 10 2010 if my journey starts from New Delhi. That is tatkal opening on 26th.
Tatkal booking is not allowed on 26th for journey from Nagpur as the journey starts on 29th. The software will allow booking on 27th.
If all the tatkal quota is filled on 26th then no one will get tatkal ticket if the journey starts on 29th in the same train.
Kindly clarify me in the matter of tatkal booking through internet for the above journey with relevant quota details/rules