It really depends. I've update some items withing weeks of receiving them and then there are some items that have been waiting in the wings for years. You'll notice on my gallery home page that I mention that I have about 30-something% online. Yeah, that's very true. I still have stuff from 2007 that I haven't posted yet. And while it's scanned and ready to go, I keep telling myself that the time is not right for me to update with it. I want to wait until certain events happen in my life, and then I'll update with those items. I suppose it's because I see the artwork as representing something due to the scene involved.
Then, there's also a large portion of artwork that I haven't updated with because I don't want the prices to skyrocket on what I collect. I don't want others to come in and jack up the prices, or take the items from me. I have a lot of artwork that fits into this group right now. I guess my thought is that, if I go six months without seeing any more items from the anime or episode I collect, then, I'll update.
But excluding the handful of items that fit in these categories, I would say that the average wait time is 1-2 years before I update with anything. In some cases, I feel that I have to make a short gif for the item, and I prefer to make gifs in the winter when I can huddle around a warm computer.
But most of the time, it's because I don't think you can handle that level of bishiness.
Light Yagami sans shirt + that delicious vampy Dmitri from 'Kurobara Alice'...I'd never be able to concentrate at work with them around!