The advantage for adult learners is comprehension and clear goals: adults usually grasp the essentials faster than children. The difficulty is fragmented time — large uninterrupted blocks are hard to guarantee.
Rather than waiting for a free weekend, split practice into three short blocks: basic technique, a passage from a piece, and sight-reading or rhythm work. Fifteen minutes each adds up to more than forty minutes a day.
Basic technique does not need long sessions; the point is to keep the motion of striking the string identical every time. Adults tend to rush toward repertoire and skip this step, and then hand shape starts to collapse as speed increases.
When choosing repertoire, pair them: one difficult piece, one you can play through completely, and one you simply enjoy. That gives both challenge and immediate feedback.
Adults rarely take up the guzheng for exams; it is usually about interest and relaxation. Slowing the pace and allowing yourself to take your time is usually more sustainable than fixing a rigid schedule.