Alright, well I rolled the dice on this a little bit after reading the fine print on Chase's "Interest Saving Balance" and concluding that they really do mean what they say - pay that amount by your statement due date every statement, and you won't incur interest on new purchases and you won't pay off special financing offers early. And . . . I was right.
The last payment of about $57k on my direct purchase was in June of 2025. The end of the promotional rate on my statements was the last day of my January statement (1/20/26 as I recall). But, the full amount of the remaining balance did not come due on my Interest Savings Balance until after that statement closed, at which point, I waited until my due date in February to pay the full Interest Savings Balance.
I just got my new statement and no interest charges whatsoever. So, what is nominally a 6 months 0% promo turned out to be 8 months of 0%. Combined with the full 60 days I got to complete my payments, I got about 10 months of 0% on my first direct purchase.
I would not advise the above strategy on other credit cards with 0% promos - I would make sure you pay everything in full by the date listed on your statement that the promo rate ends. But, Chase does appear to mean what they say with their Interest Savings Balance.