Determine average time between dates (change)

One of the items we're trying to improve is change lead times. Creating change requests, when possible, well before the expected start time. This way the change is visible to our CAB members and can be reviewed/discussed/planned to ensure success on the first attempt -- AVG lead time by change type

There are two fields I'd like to compare: Change Created Date & Scheduled Start Time

The other is trying to see how long a typical CR waits before approval -- AVG approval time by change type

There are two fields I'd like to compare: Recommendation Requested & Recommendation Received Time

any thoughts on creating a widget or a report?