It varies but ensure your best odds by... 1 completing Nightfall 2 wearing shader emblem and class item (if you have them or as you can purchase them) 3 taking on all IB bounties, even the ones you might feel are too difficult. 4 using the IB buff From there it's a matter of equipping the best armor and weapons for each map. You could get to rank 5 in perhaps 6 hours across 3 days worth of bounties and wins.