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You can create a queue, close it for all hours save for 15 minutes on a day you won't need the speed dial (say, Sunday from 2am - 2:15am) -> Call Handling and Forwarding -> After Hours -> Forward to external number -> enter the number.

There is a limit of 100 call queues per account, so this may not work if you have multiple in use queues and/or over 100 #s you need as speed dials.

This is actually a brilliant idea (Speed dial with a defined number) . This will actually save time in calling most frequent or emergency numbers. But as per I am concern its still not there in the system. If you can create this as an idea on idea portal, I think RC team can look into this as a future implementation.