How long before marketing actually starts working?
It's not even something we can guess properly, and anyone giving you a confident number is making it up.
Because it depends on what you're doing, what you're selling, how long people take to decide, and whether anyone's heard of you.
Roughly, though. Paid ads can show you something in days, and it stops the day you stop paying. Outreach takes weeks. Partnerships take a month or two. Content takes six months to a year. SEO takes a year or more.
But the bigger variable is your sales cycle. If people take three months to decide, then nothing you do this month shows up for at least three months, no matter which channel it was.
So the honest answer is that the fast channels are rented and the slow ones are owned, and most businesses need both running at once. What kills people is starting a slow channel, expecting a fast result, and quitting at month four when it was about to work.