Seat Allotment RAC against confirm ticket

Hi All,

My question is this after what time an confirm ticket(seat) will be allot to RAC passenger after trains schedule departure


Explanation about question
I have 2 ticket from allahabad to new delhi in sleepar coach train arise from allahabad jn and finish to new delhi. due to some region I couldn't reach allahabad station then I cought train at next station which is 117 km from allahabad and journey between ald - ftp is about 1.15 minute.
when I cought train from fatehpur . what I see is that my seat has been alloted to RAC passanger
So any one please tell me seat allotment time if passenger not arrive at their seat

If some one does not board the train at the mentioned boarding station, the TTE has the right to allot that seat to a RAC / Waitlisted passenger.