Her sister's candies are all stated to last an hour. Sure, if you happen to be unnaturally resistant to being drugged, it's a given that you'll be less effected.

There isn't an antidote, as they're more drugs than they are conventional poisons. A medical-nin with the know-how could probably go hard and reduce/nullify their effects, but this is the same with any other attack, so it's sort of a given.

The fact that it can be hidden in food doesn't change the fact that you're an idiot for eating any food given to you by a kunoichi. Why do you think everybody in Naruto eats at the Ramen guy's shop? He probably has a ninja seal of approval saying that all his food is legit.

EDIT: Their limitations are all stated, unless you want me to include things like "Can't be swallowed in a vacuum" and "Isn't capable of rapid teleportation."