long time user here, over 5 years of Skritter subscriptions. I have about 3200 Skritter-known characters and over 13,500 “words” on my word list.
I ran into your problem some years ago and used to get quite morose about the impossibility of catching up if I had missed days or weeks of Skritter review. That was in the days when I needed a minimum 1 “Skritter-hour” a day just to keep up with new vocabulary.
Since then I have learned that using the “advanced study” mode (on the original app) and selecting the most recent lists, and studying for ideally 1/2 hr or absolute maximum 45 Skritter-minutes a day is the way to go, no matter how many older words I may “lose” in the process.
That is because I am in this for the long-haul, disagree with the mastery of the massive vocabulary lists that Mandarin classes expect weekly, and have learned that I can trust the algorithm of the (original) Skritter app to keep me going.
You will forget older words. For that, make it a habit to every once in a while review older lists. The most important thing is to expose yourself to as much written and spoken Chinese as you can, as a native speaker does, and that will help reinforce vocabulary you have already “learned” and “forgotten”.
Some advice on your Beijing trip and keeping up your writing skills.
One, don’t worry about keeping up with Skritter reviews and instead focus on as much oral and aural practice as possible while in Beijing. Keep a note of new words you hear on the street, with friends etc., in a little pocket book (with pen) - enter them into Skritter lists when you get the chance or on your return. Converse as much as possible with everyone you meet. Strike up conversations with cafe owners, people at bus stops, and make friends everywhere you can. What is precious, from a language point of view, about your time in Beijing is the ability to immerse yourself in a Mandarin environment. There is the rest of your life to improve your reading and writing skills, but this chance to use and enhance your Mandarin speaking abilities cannot be matched back home.
Two: noticing that I was losing my ability to write characters the more I communicated with Chinese friends on chat apps (using pinyin), I asked my friends if I could go back to old-fashioned hand-written letters to communicate over Line and WeChat once I returned home. I sent snaps of my letters, and they would answer digitally. I told them not to correct my grammar etc. because I didn’t want my letters to become a burden. I just wanted practice. I’ve noticed even my Chinese friends are slowly losing their ability to recall how to write characters given social media input methods! This is much worse for the non-native speaker. Letter-writing has made a big difference over the last few years, and I’ve become much better at sentence structure too.
All the best on your upcoming trip!