There are two different clocks running, and conflating them is where most disappointment comes from.
The fast clock: technical fixes
If pages are not indexable, canonicals are wrong, or the site returns soft 404s, fixing that is engineering work measured in weeks. Google then needs to recrawl, which for an established site is days.
These changes can produce quick movement, but only because something was actively broken. Fixing a broken thing is not the same as competing.
The slow clock: architecture and content
Building a topical cluster and earning rankings for commercial queries takes months. The index has to discover new pages, evaluate them, and — this is the part that cannot be rushed — observe how users interact with them.
Three to six months to meaningful movement is realistic for a site starting from a reasonable technical baseline. Highly competitive categories take longer.
What you should see meanwhile
Even before rankings move, you should see leading indicators: more pages indexed, impressions rising on more queries, and improving average position even where you are not yet on page one. If none of those are moving by month three, something is wrong with the approach.