How careful do we need to be about sun exposure after a hair transplant?

Sun exposure does not harm hair or hair follicles.  Sun exposure precaution is for prolonged exposure that may discolor the skin.

It is important to not get excessive sun exposure until the hair is in good condition. You don’t need to worry about short intervals involving walking across the parking lot to your car but if you are going to sit out at a ball game or work in the yard or polish the car, then you need to protect your hair. If not taken care a serious sunburn may stop new hair from growing.

Light is actually a very good thing for the body.  The key is to avoid burning your skin.  Sun burns lead to all kinds of skin problems, but a little light is very positive.  You can walk to your car.  You can go out in the sun.  You must avoid burning your skin.  Burning your skin risks the health and survival of grafts.  Because you may not be aware how much time you spend in the sun, it is often a good idea to consider wearing a cap and even using a sun screen on your head. No one enters the sun with the intent to burn their skin.  Sun burns just seem to happen.  Remember this until your hair grows in for the health of your grafts.  Remember this long term for the health of your skin.  

As long as you do not stay under the sun for 10-20 minutes a day, you would be fine.
Longer periods may cause discoloration and we strongly recommend our patients to stay away from direct sunlight and sunbathing for a month.

There is a degree of common sense here as you should never have too long in strong sunlight for your skin. General walking out into the sun is not going to be a problem. But avoid prolonged time in strong sunlight. Wear a hat or cover your scalp especially in the fist few weeks post hair transplant. But also in the coming months take care not to burn or impair your skin quality over the grafted area. 

Wearing a hat is going to be important. I don't think that there is a cumulative cut off but being outside all day in Orlando is probably not a bright idea. Being outside long enough to sweat is probably also not a great idea. 

Hello. Walking across the parking lot is in no way going to be enough exposure to the sun to affect anything. It is difficult to say what the proper exposure to sun is for you since. If you are fair then obviously you cant be in the sun for very long without sunscreen, a hat, or avoiding it completely. Use good common sense in this case.

Usually laying out in the sun for many hours after the procedure is not recommended for two weeks. However going out and doing casual activities under the sun is ok. 

It is important to protect the transplant for the first 2 weeks but only if exposure is prolonged. This means being outdoors for hours. However, normal sun activities like being outdoor to run errands etc is normal. 

The warning about sun is directly prolonged sun exposure like lying around on the beach. Walking to the car and the like is never a problem with sun