I’ve been doing laser treatments on my bikini and I’m happy EXCEPT that they’ve changed or "clarified’ the rules on me and now they are no longer treating as much as they once did. 
As a result, I have a few more fine hairs in the pubic area that are not treated (they are much, much more sparse and finer than they used to be).
How long should I wait after plucking these hairs so they are in the growth cycle?
Hair grows 1/3 of a millimeter a day or about 1/2 inch per month. I am sure you have seen pictures of people with hair that starts at the forehead and goes down to the floor or longer. This means a single shaft of hair has grown about 6’ 6", consequently, this hair has grown (anagen cycle) for 13 YEARS. I have eyebrow hairs and forearm hairs that are 3.5 inches long. That means they grew for about 7 months before going into catagen phase. I also noticed they stayed around for 2 years before vanishing (falling out or being chafed off from everyday friction of showering, putting on clothing, scratching, and whatever.).
Consequently, there is NO ACCURATE number as to how long each part of the cycle is. There are numbers thrown around as to how long each of the 3 parts are expected to be, however, it also appears that this varies wildly between each person, on different areas on the body, and for each section of the complete cycle. It also proves there are very few people who care or this study would have been figured out years ago. The fine sparse hairs you allude to may be new hairs that have not yet reached their full maturity. Just as other hairs grew in fine and eventually grew coarser and longer you will find the same thing happens with your hair. It as been shown that the heat of the laser can cause dormant follicles to start growing and you may be looking at entirely new hairs that have never been treated. If you ever had a cast on a broken bone (ask someone who has) you will note that when the cast is removed there is a load of hair where there was never any hair.