Cold atmospheric plasma (CAP) is a non-thermal ionised gas that generates short-lived reactive species. We tested whether a brief CAP pre-treatment makes biofilms more antibiotic-sensitive, and how long that effect lasts. Using simple, well-controlled biofilms of Staphylococcus aureus and Pseudomonas aeruginosa, we coupled immediate post-exposure phenotyping with time-resolved multi-omics (lipidomics by REIMS, RNA-seq, proteomics; minutes to hours). Short CAP exposures (~90–120 s) consistently sensitised biofilms, yielding up to 512-fold reductions in the minimum biofilm eradication concentration (MBEC), with a clear class pattern: strong synergy with ciprofloxacin and tetracycline, minimal effect with amoxicillin. Early (minute-scale) signatures showed matrix collapse, phospholipid loss, and oxidative-stress activation (increased catalase/peroxidase/SOD) with ribosomal/translation instability. This respond  waned over 1–4 h and largely re-normalised by 24 h, defining a transient therapeutic window. Mechanistically, synergy reflected two linked processes observed across datasets: (i) rapid matrix/membrane disruption that improves antibiotic access and (ii) temporarily reduced detox/repair capacity that amplifies ROS-mediated lethality. Initial hits from the Nebraska S. aureus transposon library and scavenger rescue support redox defence as a rescuable node. Therefore, CAP acts as a fast, reversible priming step that makes biofilms briefly antibiotic-sensitive. Defining this window and the underpinning pathways enables schedule-aware, stewardship-aligned cold plasma–antibiotic regimens for recalcitrant infection.