Product and Software: This article applies to all Aruba controllers and ArubaOS versions.
ARM min-scan-time is set by default to 8. That means that every valid channel in the band must be scanned 8 times before the AP can decide to move there, even though it may find that the channel is better earlier.
To speed up convergence, you can lower this parameter, however, it is set to this default for a reason. Assuming a default ARM scan interval of 10 seconds and scan time of 110 milliseconds and 2.4GHz with 11 valid channels in the regulatory domain, it takes ~15 minutes for the network to start to converge.
(10 seconds times 11 equals 110 seconds. You need 8 passes, which is 880 seconds. Divide by 60, which is ~15 minutes.)