lights on or off?

I would think it should be the same as for any baby chick, which is 95 degrees the first week, and 90 the 2nd and continue to drop 5 degrees each week.
I have never raised meat birds, so if its different for them, someone will post to let you know
but as babies, they will not be able to survive the cold northern nights without heat.

 

It depends on how cold it is. They will feather out quicker if they are a Cornish X but they still need heat. Just like caring for any other chick except they grow faster & (based on what I've read) need the vitamins more then the other chicks.

If it is just one of the rangers then it is just like any other chick.

 

I'm a first time meat grower too (cornish X) - about 4 weeks into the process. I have had the light on (100 watts) since I got them home. First week and a half in a brooder in the basement and then transferrred to the coop (8'x6')with lots of straw insulation. They have started to free range in the daytime and sprawl out in the sun, but on cool days they will go in the coop and warm up under the light.
When night falls, they follow the light from the coop and jump inside.
I thought it might be cruel and unusual to keep the lights on 24/7, but they seem very happy and are growing incredibly fast. Sleeping with the lights on isn't a problem ans there have been no predator problems. I've noticed the temp as low as 58*F in the coop at night ( we are in Canada too) and they aren't piling onto eachother for warmth, so I assume they are happy.
And also I can see what I'm doing if out there at night.
My birds have 'feathered out' a lot quicker than I thought. I think that by about week 4-5 you could safely remove a heat source as long as the temps don't go too extreme and they have a dry draft free housing. I'm planning to turn the lights off starting next week (week 5 or so) and then send to freezer camp at week 10.