What qualifies for addiction?

That's gonna largely depend on what thing we're talking about. The short answer is: if you're prioritizing that thing to the detriment of other responsibilities and/or relationships, you're probably addicted to it.

Depends what it is and your personal tolerances, possibly including mental state and disposition.

Chemical addiction is different to some kind of mental compulsion to do something, though both can be troubling to life and general well being and informally will be called addictions.

Chemical has a few extras (mainly chemical withdrawal if you stop, and not all chemicals are chemically addictive*) but in both cases it is when something interferes with your life and general well being that you are possibly addicted. This will be things like routinely not eating, skipping out on social events to do it, it causing you not to be able to perform at work/school, not looking after yourself (not bathing, not eating, not sorting your meds if you have any), forcing through pain to do something, feeling compelled to routinely check, being alarmed when it goes wrong (or fails to go well) despite no particular reason, being distressed if not doing it, it causing financial hardship or considerable cost (you might be rich after all) to maintain, your actions causing distress in others and so and so on.

*when people say weed is not addictive this is what they mean. If you stop opiates, nicotine, alcohol in some cases, caffeine and so on you get sweats, shakes, sleeping problems and often far worse (stopping smoking will probably not kill you, stopping an opiates or alcohol habit might). It is possible to enjoy or come to depend on weed so much it distracts from life in general but the physiological basis is different.

It is quite a profound thing so dodging a shower, blowing off homework and forgetting to eat one evening whilst staying up late because a new game came out and you were interested in that is one thing, and instead the routinely part of the earlier bit is the key word so if is goes on for a protracted period (no set number of days and there are other markers a medic would pick up on) and you continue despite RSI in your arms rendering you in serious pain, or maybe the numbness/weakness part of that condition, then that is when it becomes a thing to properly note.
For the mental thing then it varies massively in what people will become addicted, even within themselves (do something at a truly low point in life and it might become the thing worth living for as it were, which is not great. Also what is done -- becoming addicted to spreadsheets if you do them for work 12 hours a day is less likely than social media as a teenage girl which is designed to be as addictive as possible -- mental distress because they did not get as many likes as someone else/a previous post/a previous day/... is not a good sign).
I do often find people throw the term around rather loosely, especially if it is a current cultural bogeyman (computer games, computers in general, binge watching films/TV shows, and social media being popular ones right now, comics were one back in the 80s and early 90s and the binge watching thing is usually only a problem because you are not taking in those sweet adverts that people paying for shock news stories happen to be selling -- nobody complains about you watching said same TV for 6 hours a night and 12 on weekends) but there are actual medical definitions and criteria. Said ones inclined towards throwing the term around are usually often highly focused on the "how long do they spend doing it" part which is probably one of the less important criteria.

@Nobody_Important4u I'm pretty sure @HylianBran is capable of looking up Wikipedia for addiction's definition. He's more asking what amount of exposure to a substance, activity, idea, etc. will get him "addicted."

@HylianBran You're gonna have to kind of define for yourself what "addiction" means. For certain religious groups, "addiction" means anything that takes away from living your life for the group for "God." For others, as @FAST6191 points out, it will be a physical addiction at the chemical level, with possible side effects for those looking to quit cold turkey that, depending on the substance in question, a person's physiology, environment, and probably a whole other host of circumstances and factors, could be fatal.

If we're talking about video game addiction, ummm...maybe make sure to take a bathroom break, eat at least a meal or two a day, drink plenty of water, take a shower...you know, the basics to taking care of oneself.

Time is not a deciding factor. It's an addiction if it's interfering with and negatively affecting your health and life (and by extension the lives of those around you). Otherwise it's just a hobby. If it's eating into your work, school, finances, sleep schedule, social life (if you have/need/care for having one) or health, then it's an addiction/obsession.

@Xzi @FAST6191 @Nobody_Important4u @Veho
Sorry, I probably should've clarified this earlier, but this wasn't made with serious intent. I appreciate the comments, it got me thinking about some things, but I wasn't being serious. Sorry for wasting your time.

It depends.
If you have a chemical addiction that you can sustain with your incomes and doesn't kill you very fast it's usually not seen as an addicion (Coffee for example). Usually people classify as addiction highly destructive drug addiction or when people can't afford to maintain their urge by themselves.