Pretty sure you can ignore IB's description, these tend to be outdated, incomplete and/or inaccurate. You should be able to cancel on ARCA until 15:59 as stated on the nyse.com link. If in doubt just test it out with a 1 share order.
I think you're right. I dug into the rule books for both NYSE Arca and NYSE and this is what I found: For NYSE Arca, the closing auction imbalance freeze begins 1 minute before scheduled time for closing auction. During this period, cancellation of MOO/LOO orders are rejected. Orders entered during this period that would mess up the imbalance would be also rejected. It doesn't specifically say this but I think this implies MOC orders can be entered/cancelled up until the start of the freeze period (15:59 ET). For NYSE, the closing auction imbalance freeze time actually begins 10 minutes before the end of the core trading session, at 15:50 ET. To me, this means you can enter/cancel MOC orders for NYSE up until 15:50 ET. The rule books are difficult for my ant brain to understand and maybe I am totally misinterpreting it but it feels like some of IB's descriptions are just wrong.