There are a few factors. WK does impose limits, but most people complete lessons slower than WK gates their progress in the first place. Others use scripts to speed up and partially work around WK’s built-in limiters (eg. using a lesson reorder script to prioritize radicals and kanji).
Reviews are a whole other side of the coin as well. Some of us use a combination of phone apps and the website to tackle reviews just about every hour as they come up, and others may only do reviews once a day.
Then there’s the issue of accuracy. I personally find that going faster increases my accuracy, since I stay closer to the exact SRS intervals and have much more exposure to similar kanji/vocab. Accuracy plays a huge role in your overall speed. Check this thread to see how your total number of reviews adjusts based on accuracy: Monte Carlo Simulation: Total number of reviews to burn everything
The fastest you can possibly go is one level every 7 days (or 3.5 days for a handful of levels later on). If I had to venture a guess, I’d say most people level every 2-4 weeks.