Advance tax payable on capital gain from unlisted shares

Dear all, I have exercised some stock options of unlisted shares in mid Apr 2017 that will be AY2018-19. I may not have any capital loss that may offset this for the rest of the year. My query is should I pay the advance tax as per the due dates 15% by 15/6/17, 45% by 15/9/17, 75% by 15/12/17 and 100% by 15/3/18 in a progressive manner or should I pay the total tax due before 15Jun2017 or immediately now?. I have come across a post long back in this forum (quoting something like Sec290) that the Assessing officer can insist on payment of the total tax due now. Thank you.