I did it over 4 weeks. I have two kids, so I spent about 1-2 hours per day. I usually did some reading or a couple leetcode problems in the morning before starting work, and a couple in the evening. Honestly, once you do about 20-30 problems, they start to feel the same. I found that if I treated each problem like an interview and slowly walked through a solution (versus just diving into code and mashing Compile over and over until I get it), the problem ends up being easier.