rel_date_diff (including custom Response Requirements) minus 'waiting' times

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I'm using rel_date_diff in conjunction with Response Requirements to find the date difference between two date fields, excluding non-working hours. This works a treat.

I have a new requirement to amend this calculation to exclude any time that the incident was 'on hold'. We do not currently use 'waiting' statuses as the fact that the customer is emailed a reminder every 48 hours is unacceptable.

I have two questions, if anyone can assist me please. We are using the November 2014 release)

1. Is it possible to prevent the system sending reminders and auto-closing incidents that are in 'waiting' status? If so, then we could perhaps look at using this...