I'm almost 100% sure about the 24 hour reset. As far as testing, I just did it this past weekend.
I would try after 12 hours, nothing... then 18 hours, nothing.... then 24 hours (right before i was gonna throw the card away) it works.
^ This trend continued on 4 of my RBC Visa d+P that had a balance after the 1st day.
BTW, a method I use to check the balance is simply go in and withdraw 60$, check the receipt for the balance and then proceed.
^ that being said, you shouldn't do that on any terminal modified tracks because it cud lead to you burning the dumps.