I have learned this about the DD's played for an ER week exit: you get in with the expectation of rising iv and the idea is to get out when that has peaked just before the ER. Fine. However, the front, short option iv rises much more than the back does - although the back rises also - but, this disparity erodes the rich P/L you think you are due. (You have to buy back the front and sell the back to exit.) Actually, if the front option iv rise is extreme enough, you might have trouble breaking even on the this DD setup. I suspect that, like most time spreads, these will make out better if the u/l falls toward the put strikes - that way the front/back disparity may not be so great.
"If The Fool persists in his Folly he will become wise." - William Blake