How long did it take you to get to 10k MRR?

I got there almost immediately after launching the paid product, but this was after a year as a free product. I spent that year developing/polishing/listening to what users wanted.
When I added the paid tier in September 2018, I restricted the free usage slightly and ran a promotion for the first 3 weeks allowing users to lock in for a slightly lower price. I did this to secure the 'superfans', bringing in about $50,000 of revenue.

I feared things would fall back after that, but revenue has consistently been between $10k and $16k, and I put this down to the time I spent building the community around the product. I also have plenty of completely free resources on the site that others promote/cross post, which brings a constant stream of new and repeat visitors, some of whom wind up subscribing.

Its took me 8 months, since launch, to get to 6k mrr. I've mostly tapped into prior relationships to help me get to this point.

It took me 8 years, but my product was a free website providing resources for students. I wasn’t really focused on generating revenue until the last two years, as it was a side project. I did build a large audience (2 million content views a month) and a well respected brand in the space over that time period. We got to 10k MRR after launching native apps on iOS and Android with a paid annual subscription model.