The time it takes for cold medicine to kick in and start working is around 30 minutes.
The time for cold medicine to kick in can vary depending on the medicine but you should start seeing results within 30 minutes to an hour.
However be aware though that cold medicine can only ease the symptoms of the cold virus and flu virus and cannot actually get rid of the cold or flu virus.
So you won't really recover any faster when taking cold or flu medicine for the cold or flu but the cold and flu medicine can help ease the symptoms and make you feel a bit better.
Make sure you're staying hydrated and getting plenty of Vitamin C such as by eating oranges, drinking orange juice etc.
There's no cure for the flu or cold and just letting it run it's course is usually about all you can do but it's okay to take some cold and flu medicine to make you feel better.