travel date of indian railway for long distance trains?

i would like to know, of which date i have book ticket from irctc.co.in website (15th or 16th) of delhi-bangalore rajdhani exp leaving delhi 21:15 15-dec and boarding from jhansi at 1:45 16-dec? i have to board at Jhansi to Bangalore.

Reservation is permitted for 60 days in advance with respect to the train starting station - lourney date not to be counted.

For your case reservation for 16 dec on that train from Jansi you could have book the ticket earlies on 15th Oct.

As of now there is no reservation available in that train till 11th January. You can try Tatkal ticket which should be collected 5 days in advance.