We have been promoting the Platinum Card from American Express and then using the Delta Airlines Get More Miles Promo for a 50% bump in the transfer to Delta for first-time transferers. The promotion ends on May 31st. That is just more than two months away. To make this deal still work, an applicant would need to apply for the credit card, receive the card, complete the required spend, have the points post (or borrow them), and then make the transfer.
I am not advocating starting now, nor am I suggesting you are too late to start. If you are confident in borrowing the points for a later payoff when they do post, you may have a chance. But I think the hope of getting everything done now by May 31st is becoming increasingly difficult.
This is meant as nothing more than wake-up call that the calendar is ticking. My points posted on March 12th on an application I completed in early to mid February and I met the minimum spend within the first billing period, which ended on March 21st. Go figure!