It's not consistent at all in my experience.I've had the same thing happen to me the last two times I tried to take advantage of the promotion and I was well under the limit. I would make two separate purchases of disney gift cards and the third would be canceled. It didn't take a month to reset, but it did take a couple of days.
I ordered in January fine. Took a break in February.
On 3/9, I ordered 2 x $50 e-gc.
On 3/10, it wouldn't let me do $50, so I got 1 x $75 mailed.
On 4/3, I ordered 2 x $50 e-gc.
On 4/4, 2 x $50 e-gc and 1 x $75 mailed.
On 4/7, 2 x $50 e-gc (and 1 $25 Starbucks).
Then I was maxed out. I took a week away; as of today, I'm still maxed out on both the $50 e-gc & the $75 physical card.