Just wondering what is the waiting period to get compensated for a missing checked bag? Say, I arrive in YYZ and my bag does not. What am I entitled to right away and what comes with a specific time frame?

Did this happen or are you predicting it?

I believe 6 hours need to pass before you are entitled to anything. And it would definitely help if you had a Credit card that offered lost/delayed luggage insurance.

Please not to be Anti-Ac however if you are expecting anything from them...well forget it. They don't pay out Somehow they don't feel they are responsible. Take it from me with lost luggage delayed luggage etc. You get AT MOSt 5 percent off the base price of your next fare(like 40 dollars) and that is it. I have filled out the forms 5 times and zippo

It is hypothetical. I was reading an article where in the US you are entitled to immediate compensation for some items on US carriers:

"It's not true that the airline has 24 hours to return that missing bag before it has to compensate you. According to the DOT, if you reach your destination and your bag doesn't, the airline has to reimburse you on the spot for items you need immediately. If someone challenges your source, cite the Code of Federal Regulations, Title 14, Part 254."

I was wondering what applies in Canada. I don't normally check a bag, but I am heading to LHR next week and will be... Planning for the worst.

Depends on where you flew from. Ex Europe, I was successful in asserting my Montreal Convention rights (since they use that to limit their liability, surely it establishes their obligations as well). They covered the cost of the things in the bag that I specifically needed during the multiple days that my bag had its separate vacation.
Expect to have to go three rounds. First round, email denial. Second round, token small sum as an exception. No email, just cheque. Do not cash it as the endorsement side of the cheque is a waiver of further liability. Ask for the remainder. Remainder arrives. No email, just cheque. Perhaps they don't want emails that can be posted on social media.

OK, so if I am reading this correctly, the county of origin for the flight defines which laws to be followed? So, for example, if I fly AC LAX to YYZ and my bag has gone to KHD , the USA DOT rules apply?

Bottom line. Don't spend anything that you wouldn't spend if you knew that you wouldn't be reimbursed unless you have express authorization from the carrier.

Immediate needs may be interpreted as underwear and shaving cream, not a suit.

Longer term, don't expect more than fair market value (FMV), not the replacement cost.

A couple of broader thoughts:
1. Lost / interrupted bag insurance is often part of CC's or certain homeowners. Many businesses have this coverage too.
2. The Montreal Convention protects the carrier, not the pax. It places restrictions on the maximum which can be claimed.
3. Don't cite laws and rules to low-level baggage people. It's a waste of your time and an irritation to the guy behind you in line who also wants his bag.

They tried to contend that my bag was waylaid on the way to my home base, and they reimbursed delayed bags only when stranded away. I pointed out I was leaving again and my suit is in the bag. Yes, I actually DID buy a suit. It was a women's off the rack outfit, and the price was well under the allowance limit of the Montreal Convention. (And there is no home-base exemption in the Montreal Convention.) I waited several days but had to pack again. So you don't think I am a bag lady, I do have other clothing, but the nature of the two trips meant that all the items I needed for the most important business events in the second trip were in the suitcase for the first.

I am not sure whether the force of laws pertain to every point of origin, but the EU government does assert the passengers' rights. The airlines may try to play dumb and hope passengers don't find out about it but the EU people even have a handy app you can carry on your iPhone to tell you the rights.

I did the complaint all online via the complaint form, and then email correspondence with the excuse-givers who answer it. The people at the airport and even the baggage tracing call line people are powerless, lack access to the information you need, useless, or several of the above, at any given time. Deal with the people who have the power.

Now, I have read other people saying "I have just landed in this foreign land and you have absconded with my toothbrush" and the airline giving them an amenity kit, so there are different kinds of problems and different levels of solutions. As I said, I was home. The airline had my makeup and my clothes, but I had backup toothbrush etc. at home.

The problem was created simply by them failing to load my bag. It wasn't sent to exotic places. It wasn't checked late or tagged wrong. They just didn't put it on the plane. For several consecutive days. They tried to say "your baggage arriving with you is something we aspire to but cannot guarantee" but when they have a bag that doesn't match the manifest, they will hold up the freaking plane for 90 minutes to get it off, so I thought I had the moral high ground and I just stood it. I do have cc insurance, but it never occurred to me to go that way: the airline was responsible.

I am not sure about the advice, Often1, about not spending without authorization from the carrier. As long as you are not spending, you're giving them evidence you didn't need the thing you are asking them to purchase for you. I would say, make spending decisions as if it was your own money, and then press for fair reimbursement, knowing that you won't get more than the legal provision (and may have to fight for that, and may end up with less).

Arriving bag-less at YYZ I don't ask for anything as I have stuff at home, but arriving at YYC from LAX or YSJ from YUL without my bag (both have happened) I just ask for the standard kit AC hands out containing basic sanitary needs (razor, toothbrush, soap, etc.) - never a problem. It looks like a zip-up washbag and has much the same stuff in it.