At the very least it should inhibit the charge and offer you the opportunity to override that.
In other cases with a 110V or 220V charger, it's highly unlikely that the battery will ever be too hot to charge unless it's 120F outside and you've been pushing the car hard.
Look, it really is a minor issue that never crossed my mind until I came across the recommendation in the manual recently. It probably will impact the battery's life only slightly, but it's easy to change the timer and start charging a bit later. It's certainly true that any heat a battery sees will contribute to its degradation, especially while charging because that also generates heat. I figured I'd pass along the recommendation as an additional way to take good care of the very expensive battery.