Sorry if my question sounds stupid but I don't really understand whether the arctic silver 5 burn-in time is 200 hours total or 200 hours of computer use? How long can I keep my computer on during the burn in period ? Is it necessary to remove the power cord when putting the computer through a power cycle?
It basically means that AS5 will not properly cure until you have used your PC for around 200 hours at which point AS5 will provide it's best possible thermal transfer to the heatsink itself. Your PC does not have to be on for 200 hours straight, just 200 hours in total.
The difference between 'cured' and 'un-cured' AS5 is something like 0.5C so not really worth worrying about.
So unless you are planning something extreme where 0.5C may make or break your project, simply use your computer like you normally would. In every day life though, if 0.5C can make or break your PC, I wouldn't want to use it no matter how good it may otherwise be.
My guess is that the reason why the AS instructions say to turn off the PC a few times during the curing process is for thermal expansion to help spread the paste more thinly and evenly, which also helps pump out excess oil (or whatever liquid is used to carry material) and pack particles tighter. All of those benefits apply to other pastes as well.
The CPU will already be cycling from 25-35C idle to 55-70C full-load under normal use so adding full power down should not contribute much to the curing process.
With 20C room temperature, CPU fan profile set to performance and case fans set to high, I can get idle temperature under 30C... but I like my PCs to be quiet so all fans are set to low-speed and I end up with 35-40C idle.
My 25-35C idle range is for people who do not mind sacrificing quiet for performance even though optimizing idle temperature at the expense of quiet is somewhat pointless.