Wow that is too bad. Overbooked but no compensation?
The Denali Grand Tour should be great. I took a similar one from the Denali area in late May.
I don't think it really matters too much morning or evening. However by late August there is a significant amount of darkness - sunrise is about 6.30am and sunset about 9.30pm. Just so long you are within those parameters, which I am sure they would be.