How long to calm down in "quiet time/time out"?

[giraffesCantDirtyDance]

When starting this with a new child how long does it take them to get it? My gut feeling is its worth persevering with this method, I can see small improvements already and starting to "get it". But just thought Id brain pick incase am missing something glaringly obvious - like a magic way to deal with it in other ways?

I know there is a minute per year guide, but I find it varies between children too. Some 'get it' as soon as they are sat down, but a 3 yr old in my care today held a grudge for at least half an hour before she came for a cuddle - not sitting in time out all that time, just moving on with our day.