Tickets must be issued by March 18. 3-month max stay. Minimum stay is 6 days or first Sunday, measured from departure from origin. No day/time restrictions.
UA flyers: This is available on United.com for people who need to earn PQDs. However, the trade-off is slightly fewer redeemable miles.
Example: VIE-HKG nonstop RT. Booked at United.com, you'll get $1618 PQD, 21,664 PQM, and 8,090 (general member) - 17,798 (1K) redeemable miles. Booked on Austrian or Lufthansa or wherever, you'll get 0 PQD, 21,664 PQM, and 10,832 (general member) - 21,664 (1K) redeemable miles. (There's no class-of-service bonus for P -- it earns 100% of mileage flown on a non-UA ticket).
Thanks, OP. ^