Only a few days. Before I figured it out better and when I had the waiting times, I was able to get 90 or so a day over a couple of hours. Then a sale hit (30% off) and I picked it up for 385 when the price was 550 (it had just been raised from 500, and went up to 750 a day or two later).
1 week right about the time it went up to 750. However, there was much more activity on the site then, so the likes came much more easily. My advice to anyone trying to get Member+ is to set a daily goal. Even at 50 points a day, it'll take only 2 weeks to get the coveted access to the loli games. And regardless of how long it takes, the lolis will still be there.
I don't go hard-core in the lurker threads but I am consistently gaining 100 LC a day. I just put my opinion out there on random topics. It took me 5 days as I bought on a sale.
I'm at a little over 150 after one day, and maybe only around 4 hours of that day. I wrote LC off when the new system was introduced because i'm not a guy who likes to post and I thought I would never try, but it's actually going faster than I thought. So I'll see it through. Seems like finishing in less than a week is feasible with a few hours a day.
About two days, although I did admittedly spam a lot and encountered the post cooldown quite a bit. And the cost went up at the end of my first day. Just go to the relevant lurkers and anti-social thread and have conversations in there. Also, don't forget to like posts to help other people in the same situation, they are likely to like your post back.