Puzzle glue with a subtle coating after 24 hours: Hasi Jigsaw Puzzle Glue
Hasi Jigsaw Puzzle Glue is a water-based PVA adhesive for preserving finished puzzles and diamond paintings in Korea. I used it on a photo puzzle gifted by friends from Taiwan and found it fully hardened with a subtle coating the next day. Verdict: a worthwhile item to keep if you want to preserve a special puzzle result.