Within my first week and <1000 playcount, I could farm easies and normals with DT+HR and achieve 90%+ accuracy FC. Within my first month and ~2k playcount I could FC easy-midrange hards. Took me around 5k playcount and 3 months until I could FC 3.5-4 star insanes, and maybe 8k and 4 months until I could FC 4-4.5 stars. Around 10k playcount, I picked up DT, mostly applying DT to 3-4 star hards / insanes, making them end up at 4.5-5.5 stars. I still can't DT these songs with decent accuracy most of the time, but I can play them well enough to get PP. (I've been playing 6 months now)
I'm fairly sure that my time / playcount to rank ratio is pretty bad, as I see people with much lower time / playcount and much better rank, but this is probably cos of my well below average accuracy, which costs me in PP massively. This is probably pretty inaccurate, as when I first picked up osu, I didn't play anywhere near as much as I do now, as you can see in my historical graph, I average at like 1k playcount per month, and slowly move up each month until I end up at nearly 4k per month.