Six pieces, six ways of moving, three special cases (castling, en passant, promotion) and one goal. I teach the lot to an eight-year-old in about an hour, and by the weekend they are beating a parent who has not played since school. That part of chess is genuinely easy, and anyone telling you the rules are complicated is remembering the diagram in a book rather than a board in front of them.
The hard part is the second thing, and nobody warns you about it. Chess is mostly recognition. Strong players are not calculating twenty moves ahead; they have seen this shape before and know what it wants.
e A club player does not work that out. They see a king on e8, a rook on a8 and the c7 square sitting between them, and the move arrives on its own. Getting to that point is a matter of volume: you need to have met the fork a few hundred times, and the pin, and the back rank, and the smothered mate.
What is quick and what is slow
Quick: the rules, in an hour. Legal moves feeling automatic, in a week of playing. Stopping the obvious one-move blunders, in a month if you build the habit. Basic checkmates, one evening each.
Slow: calculation, which needs you to hold three or four positions in your head at once. Endgames, which are exact and unforgiving. Judging a position without counting, which is what people mean by intuition and which comes only from playing a lot of them. Openings are somewhere in between, and matter less than everyone expects.
Thirty days, if you want a number
Here is what I would give an adult starting from zero, at about forty minutes a day.
Week 1: learn the rules properly, including how you capture and the three special moves, and play 10-minute games without worrying about results. Week 2: 20 tactics puzzles a day, and king and queen against king until you can do it every time without stalemating. Week 3: opening principles only, no memorised lines. A centre pawn on e4 or d4, knights to f3 and c3, castled by move 10. Week 4: keep the puzzles going, play 15-minute games, and after every single move your opponent makes, ask what it now attacks.
Thirty days of that and you will beat the version of yourself that started. Chess tactics for beginners covers the patterns from week two, and how many puzzles a day is the honest answer to the question everybody asks in week three.
The bit that actually feels hard
Losing. You will lose half your games forever, at every level, because the rating system arranges it that way, and beginners take that personally in a way they never do with tennis.
The fix is to stop measuring yourself by results and start measuring by blunders. Count how many pieces you gave away for free in each game. Three, then two, then one, then none: that curve is what improvement looks like, and it moves a lot faster than the number next to your name.