Re: When to take a weight gainer?
There is no real answer to your question, it's mainly just a personal preference and a lot depends on your own preferences, body-type, and lifestyle.
If you are taking this weight-gainer because you "truely" are a hard-gainer who is eating 5-6 meals a day and taking in a huge amount of calories, protien, carbs, etc. and still not gaining anything. Then this advice might help.
Supplement your meals with a 2-3 shakes per day. You might want to have one before your workout, one within the 30mins following your workout, and sneak one in right before bed. Don't be fooled though, these calories while high in protien are not as good as real food sources so REMEMBER TO EAT, EAT, EAT.
If you are not really a hard gainer, and just looking for something to fit in some extra calories and protien then you can save yourself some time and money and just have one within the 30 mins after your workout or once before bed. This will add some calories and nutrients to your diet without too much added fat or sugar. But IMO, if you aren't a hard gainer just force yourself to eat the 5-6 meals a day and grow that way.
Again, these are just my opinions/preferences and are subject to redicule from others.
Best of luck,