In a previous life i used o be a chef for 15 years so i've cleaned lots of these.
Ladder etc it depends what below the canopy, i'd try and work off that as there will be allot of scrubbing involved.
It's not an easy space to clean and You will find yourself bending over backwards.
The grease sticks to the canopy, probably quite thick if they are getting you into clean it.
You will need to spray something to cut through the grease, you may need a scrapper.
There is generally a ledge all the way around that's full of grease.
As for time it's hard to say without seeing it, but whatever your thinking you can probably double it!!
As for baby oil do not use this in an industrial kitchen it's a breading ground for bacteria not good
Hope this helps a little
sarah