How long did it take?

Four years!

I build the site in a day and then abandoned it. I didn't want to invest time in it because I thought the market was too small. Surprise, no sales came.

A few months later, I came back and did some SEO work. Sales started to trickle in. Very slowly.

Every 6 months or so, I'd come back and update the site or raise prices. Sales slowly increased over time. I mostly left it alone because I was working full time and spending my evenings focusing on other product ideas.

Once it started outperforming my expectations, I decided to give it a second look. I did a big redesign and overhauled the products and prices, which doubled sales overnight.

Three months with my first app. Four months with my latest.
All effort was organic SEO (Keyword research, Page Copy Tweaking/Onsite Tweaks, Link Building - that's the hardest).

6 months of full-time-no-social-life-commitment.

About 7 days. We hit a very hungry market early on that had a huge amount of word-of-mouth referrals. We gave free memberships to about 10-15 people in the beginning who we knew had large networks. We focused on making them extremely happy so they would refer us.

It was many months of about 10 hours per week effort for me.

Launched a new backlink service/database on February 25th. Today is exactly one month since the launch. Already earned $2364 in the first month.
Here's the proof from my dashboard in Wordpress: https://i.imgur.com/nmLbw3Q.jpg