ChaRM - Customizing Admin Change Document

I've added the Request Start field as shown in my ZMAD document below.

I'd like to add the following, but I don't see any obvious fields available to add when using the configuration tool.

Duration - (calculated from Requested Start and Requested End)

Downtime Flag - This would be very useful to indicate if downtime is required for the admin change.

Has anyone done something similar?

Thanks,
Roy