You can filter out unwanted statuses from resolution time calculations by adding additional filters to the Resolution Time metric.
Clicking on Resolution time will open the editing window for this metric. From here, click on the Add Filter option on the right of the Timer is running when section.
For this type of set up, you will want to select the Status filter type. From here you can select the status, or statuses, that you would like to include or exclude. The example below has the Waiting on Requestor status selected and is using the Exclude Selected option to remove this status from SLA calculations.
Once you have selected your status filters you should see them displayed in the Conditions column of the Resolution Time metric. Be sure to click Save before leaving this page.