Payment of advance tax on LTCG?

Property sold in May 09 with liabilty for LTCG. Having second thoughts on investing in a flat, but decision can be taken only by mid November 09. Can I combine and pay the advance tax of Sept. 09 alongwith December 09 if undecided by then on buying flat? What would be the penalty for delaying this payment by three months. I am a senior citizen with only bank interest income of around 2 lakhs for current FY.