It doesn't take long for the bulldog to learn that barking brings a person. I know of one dog who had slept through the night, without a problem for many years until one night a particularly loud thunderstorm woke her and scared her enough to try and escape from the kitchen. The sleeping owners heard her scratching at the door and realising she was terrified of the storm went down stairs to comfort her. The next night at the same time as the previous nights thunder storm, she began scratching at the door, she had learned during the storm that if she scratched at the door someone would come to her. Sure enough the owners went down stairs to tell her to be quiet and that set the pattern for the next night and the next and the next. This clever little dog had learned what brings a person and this is what happens with most learned behaviour and the only cure is to ignore them. Sadly, what is learned in one night takes several nights, sometimes weeks, to unlearn.
Most barking behaviour is set along these lines, to the dog the simple act of barking brings a person and night time barking almost always works because most people don't want their dog barking in the night disturbing the children and the neighbours. Day time barking can last all day because in the dog's mind, if he keeps it up long enough you will eventually come back - he has no idea what time you finish work or what time you would walk through the door anyway, they simply know that eventually their barking brought you back.
All dog behaviour is learned through association; once an association with a specific behaviour has been formed it stays with them for ever. Just like the dog that learns that growling keeps them their sofa, they're not necessarily an aggressive dog - just a clever one, and the best way to break this behaviour is to change the association. Work out what your dog sees as his reward, does barking make you appear? If so the easiest way to deal with it is to simply ignore them but that's not always possible, especially in built up areas or in homes where there are children sleeping or adults that have very early starts. If you must go to the dog, the arrival of you must not be a pleasant one, so no silly voices, no cuddles just a firm NO and the use of a water pistol usually does the trick (although there are some dogs that view the water pistol as a game).
If your dog barks during the day it's important that you wait until they are quiet before you walk through the door so the association is formed with the not barking that made you appear.
Training collars can sometimes work, DO NOT use a shock collar, they are cruel, but collars that omit a high pitched whistle or a jet of lemon spray often work very well as it's the act of barking that triggers the collars and again an association is formed between the bark and the punishment.