At the risk of sounding critical, I am a little annoyed. I understand that everybody works at different speeds, but I am interested in what other people's experiences are, what you have done.
I also get the feeling that many people here either have false modesty, or are very self conscious of their work and at the same time their biggest critic.
I find jeanwilson's suggestion on waiting till one has no longer needs the exemplar helpful. Thanks.
I just think everyone IS giving their honest opinion in this thread (assuming false modesty being that they believe they are better but put themselves down to appear humble), and self perception is subjective. They are explaining why it can be counter productive to put a number, because as you go along, this may change. Impatience never helps. Some days you can spend a lot of time writing and dislike everything.
If you really want a general safe estimate for starting new scripts, I recommend giving it 2-3 years (3 is better) of starting until you are sufficient in whatever script you start with, enough to understand the foundation rules of calligraphy (posture, the discipline, drills etc etc)because this will be applied to all different hands), and you know what the proper script should look like, such that you can conjure the image of it in your mind, reproduce it with your nib and it's not an image that differs greatly from the piece of exemplar. But I will recommend to keep coming back to the exemplars, and to pick better exemplars, as you get better trained eye to tell the good from the not so good ones.
I can imagine how spending a few months on different scripts at once when you're new can lead to confusion and mixing up of scripts, like applying different rules to the wrong script and things like that. That happened to me when I started out with copperplate then tried too early to jump to Spencerian and then later get back to Copperplate and Engrossers. When I first started with Spence I worked on it daily for 3-7 hours, non-stop for about 2 years and only relaxed in the third year before slowly going back to Copperplate to refine it. I skipped socializing, lived and breathed the Spencerian script the first thing and last thing I saw, and I printed out books and exemplars to stick it in office (i still do) and have pictures in my phone and folders), I worked on it during lunch, doing circular drills with pencils, pens.. I pored over the materials on trains and buses. Is that what you're asking? That's what I did on my journey. The amount of time spent is important, but using it productively is important too.
I'm not sure about you. I learn best visually, on my own than having a teacher hover over me. Some people learn better with teachers. I set small goals of things I want to refine for weeks for one thing at a time(like working on the top of the lower letter r, or trying out a different form of f, working on the belly of the lowercase S, working on writing at 3mm, 5mm x height, working on g, j, k, l loops), comparing my writing to exemplars (which is why i stress never ditching exemplars).
Hope it helps.