Churning data point:
Just figured I would share: Got my first Visa Signature card with the 25k miles upon approval offer on Nov 21st. I've hit the card hard with the MS probably putting $25k on since I got it.
On Feb 23rd, I applied for a second card (using the 25k points and $100 credit after $1k spend) and was approved instantly. I counted and it was around 92 days after first card was approved. I plan to put some spend on this card, but cancel after two billing cycles - will try for another one in May and report back.