Allow tasks alerts to be sent to external contacts at dedicated time not automatically.

Our IT support assist with the onboarding and offboarding of employees. Currently you can assign tasks to users of the system based on a number of days prior to/after start date/leaving date. However for external contacts you have to select the email option which eliminates the ability to send based on the trigger date and they are automatically sent immediately. The concern is that where the notification is triggering immediately it may get forgotten about. Ideally we would not want to have to add our IT contact as a user to the system so would like to utilise tasks for email the same way they work for users of the system.