Just two or three days - make sure you have sufficient water and that it is secure so that it could not tip over and drain away. Generally I only feed enough for the day, but if gone, I set up a self feeder, set it up a day or two ahead of time, to make sure it works. I leave the chicken door open all the time, so no change there.
If I am going to be gone more than that - I have someone else check on them. My biggest fear is water.
Mrs K