You will hear conflicting reports here as to when to take it:
(1) everyone will agree that it should be included in your final meal, just before bed with a slow releasing protein
(2) everyone will agree that it should not be eaten in your PWO
(3) most people will agree it should not be eaten with refined carbs.
(4) where the controversy is, is whether it should be eaten with carbs on a cutting diet (i.e., with things like sweet potatoe etc) because it may increase the release of insulin. My personal opinion is that if this argument was accepted, i.e., you cannot combine fats with carbs, people would not consider oatmeal healthy, (which is 10% fat) and yet it is a stable of most diet. Further, since EFA's are very slowly digested, I think its fair to say that having 1-5 tablets with a meal containing good carbs will not lead to an excessive insulin spike.
As for quantity, this depends on how much fat you consume in the rest of your diet. Ideally, set a target for the amount of fat you wish to consume, and consume as many flaxseed oils as you want without exceeding the fat limit. If you eat lots of fatty fish (salmon etc), you won't need to consume as much flaxseed oil. Personally, I consume 10 grams of the oil per day on a salad at night.
You should be warned though that excessive omega 3 intake will cause a omega 6 deficiency if you consume little omega 6 - try to work out how much omega 6 you consume, and ensure the amount of flaxseed oil your consuming is not excessive relative to the omega 6 (evening primrose oil is a good source of omega 6). Most people consume too much omega 6 though (soybean oil etc)