I personally find the 'cancel build' button text confusing; it isn't time-bound. I suggest changing it to 'Cancel pending build'.
Relatedly, if Foreman knows the host has been built, I'd suggest this be changed to 'rebuild' and 'cancel pending rebuild' to make it more clear what is going to happen.

I don't see any prominent notice on the host status dashboard saying, Rebuild will occur automatically on next reboot -- which would be nice. Perhaps changing the colour of the 'cancel pending rebuild' button would double to provide this status without taking up more real-estate.