It really depends on how obsessive you are
Whether it's baby chicks or adult birds you need to tend to them at least twice a day... morning and evenings for feedings and cleaning up waste, etc.
With the chicks...Setting them up so that the light (heat source) is in the right place, etc. Just getting set up takes time gathering supplies.. not to mention reading up on everything. You can see why this website is so busy!!
With older birds that can be outside.. well, I still check on them no less than twice a day (or when I hear distress calls... my rooster sees something and calls out at least once a day sometimes it's a neighbor cat I have to chase off). Check water, food, and little clean ups where needed. Occasionally spending time reinforcing the coop and run... Oh and yeah... the time and material needed to build the facilities. You can be super organized and prepare way in advance or like me.. I just have adapted and learned and figured things out as the need came up.
Over time it becomes 2nd nature and requires less time commitment. You'll know there are message boards like this one to go and ask questions or help others.
You'll also find them relaxing and pleasant pets to be around. I enjoy it when I'm letting them freerange and I go outside and they all come running and flapping and flying toward me. then they follow me around when I'm working in the yard. It makes yard work lots of fun. I was up on a ladder the other day and my fave EE hen flew up and perched on my shoulder for a visit.. it was sweet! They like to jump in my lap to be pet and eat out of my hand and it's really neat.
In general, they can take a bare minimum of time once established or when you have free time you will probably find yourself outside enjoying them. It's a great way to a start of the day, and end the day... hope that helps! But you won't know how it will be for yourself unless you try.