By peak time, I'm assuming you mean the times when most Colombians are out on holidays and many parts of the country are full of people. You will be arriving in late November and leaving in early December, so you'll just miss the high season here in Colombia. It doesn't really begin to kick into high gear until late December, so you shouldn't have to worry about the hordes.
You'll always find people in the hostels no matter the time of year. Sure, different countries and parts of the world have different times they take vacation, and depending on the time of the year you may bump into more people from a particular country/part of the world, but you'll always generally find other travelers in the better hostels.
Actually, the time of year you've picked isn't too bad. Just stay in a decent hostel and you'll definitely meet other people. I think it depends more so on the place you stay, rather than the time of year. I've stayed in a hostel full of people one day and the next in another hostel so quiet that you could hear a pin drop. Popular hostels are generally always busy.