Centre, VH-ABC, commencing descent XXX in 3 minutes
Thats what you're taught in your IFR training. No-one does it in the real world!
It's much quicker and easier to say XXX TOD XXX Request traffic. Followed by an all stations broadcast.
There is a reason why we do this. In our descent checklist it has 'altitude alert' and PF responds with the LSALT which has been set after traffic is received. If we have not got traffic by that stage then a quick call to centre is initiated.
Sometimes if you just say "XXX, commencing descent XXX in X minutes" you will get the reply from centre "XXX copied no additional" when you have not received traffic in the first place. It's much faster and easier for us to preempt them IMO.