That depends on you, the hacksaw and your patience. You will probably have to use just the blade without the handle to be able to get to the bolt. It should be brass which cuts fairly easily. 1-2 minutes should be enough.
Safety precautions for using a hand hacksaw include, using the right blade for the material you are cutting, wear goggles and safety gloves. You should also hold the handle securely and make sure the material you are cutting is secured and will not move around.