Flash sale, only while it lasts - snooze and lose!
Tips
register
Everywhere in marketing copy: 限时优惠 (limited-time offer), 限时免费 (free for a limited time), 限时抢购 (flash sale). The urgency framing - pair with 仅剩 (only X left) or 倒计时 (countdown) - is standard e-commerce technique.