The amount of time you need to cold smoke your meat will depend on several factors: ultimately, how smoky you want the overall flavor, as well as the type of meat you are trying to cold smoke. For bacon for example, it can take anywhere between 6 to 5 hours for a light smoking, and anywhere from 25 to 50 hours for a heavy smoking.
It is always best to err on the side of caution and try not to use too much smoke, as this can leave you with bitter tasting meat that isn't all that tasty at all.
When it comes to smoking fish such as salmon, you should use this general rule of thumb: cold smoke your salmon for between 4 to 6 hours for a light smoking, and 12 to 24 hours for a heavy smoking.