Anywhere from a few minutes to several hours.

Some of the factors that will affect how long it will take:

• The temperature differential between outside and inside.
• The thermal efficiency of the container holding your camera. A ziplock bag will have almost no insulative value. Some camera bags or high-end cases, on the other hand, may have a moderate to very high R-value. Although both should protect against condensation, heating the camera up more slowly will protect against thermal shock that can affect electrical soldering points and even the bonding in printed circuit board components. (This would be more of an issue over many, many repeated occurrences than for a handful of times on a single trip.)
• The mass/weight and size of your camera. The larger and/or denser it is, the longer it will take for the camera to fully warm internally.
• The amount of airflow over the bag containing the camera, as well as the relative humidity of the air. Moisture content of the air affects the exchange rate of heat between a surface and air.
• How long your camera was outside. It may not have been fully cooled internally if you were only outside for a very short time, especially if the camera was turned on and producing internal heat.

As others have already said, this is a time to be patient. It's not worth the risk to your gear to get in a hurry. Don't open the bag until you are certain the camera has fully warmed to room temperature, then give it a few more minutes (or even another hour or two if the temperature differential is very large) to be sure the internals of the camera and lenses have also warmed.

I normally use a backpack with plenty of padding to carry my camera. Of course the padding is mainly there to protect the contents against bumps. But it also provides some insulation. If I'm shooting outside when it is cold, I always bag everything outside before carrying it inside.

If the bag and cameras are outside for several hours in sub-freezing temperatures around 20°F-30°F (-7°C to -1°C) and then brought inside to temperatures around 65°F (18°C), I set the bag down and don't even think about it for at least a couple of hours.

If the outside temperature is below freezing and I take the insulated camera bag from inside at room temperature, put it inside my car, drive to a shooting location (while heating the car's interior), and then walk for several minutes from where I'm parked to an indoor shooting location, such as a school gymnasium, I try to give myself time to allow for at least 15-20 minutes before I open up the bag. Gyms tend to be very humid when there are lots of folks in them and both the fans and athletes are very active and perspiring.