The honest timeline is slower than the marketing and faster than the despair. What frustrates most people is not the rate, it is that the first month produces the wrong kind of progress.
What actually happens, in order
Weeks 1 to 4: neural. You get noticeably stronger and almost none of it is new tissue. Your nervous system is learning to recruit what you already have, coordinate the movement and inhibit less. This is why beginners add weight weekly and look identical.
Weeks 4 to 8: the transition. Measurable protein accretion begins. Muscle glycogen and water increase, which does change how you look, though it is not the thing people mean by muscle.
Weeks 8 to 12: real change. Genuine increases in cross-sectional area that would show on a scan. Usually noticeable to you, often not yet to anyone else.
Months 4 to 6: visible. The point at which other people start commenting, which is the milestone most people were actually waiting for.
What determines your rate
Training age. The largest factor. A novice and a five-year lifter doing identical programs will get very different results.
Total weekly volume per muscle. The dose-response is real up to a point. Ten to twenty hard sets per muscle per week covers most people, worked through in how many sets per muscle per week.
Eating enough. Protein around 1.6 g/kg, and enough total energy. This is where most people who train hard and see nothing are actually failing.
Sleep. Short sleep measurably impairs the response to training, and it is the most commonly neglected variable in the list.
Genetics. Uncomfortable and real. Response to identical training varies enormously between people, and comparing your rate to someone else’s is not informative.
Why the first month feels like nothing is happening
Because the change is neural and you cannot see your nervous system. The useful response is to track load rather than the mirror: if the weight on the bar is going up, the program is working even when nothing looks different.
The mechanics of making it keep going up are in progressive overload, properly explained.
On the protein side, the protein calculator does the arithmetic, and the reverse question is how long it takes to lose fitness.