How can I measure resolution time for a ticket excluding the time spent on waiting for the customer?

You can get this data in two ways:

1. Choose the Metric: Resolved time spent in business hours
Sort by Filter: Status does not include waiting on customer
Group by: Status
From underlying data, you can find out how much time was spent on the SLA status at a ticket level

2. Choose the Metric: Resolved time spent in business hours
Sort by Filter: Status does not include SLA Status: Off
Group by: Status

From underlying data, you can find out how much time was spent on the SLA status at a ticket level