In order to redeem the discounted rates, travel has to be scheduled between August 22 and December 17 of this year, which doesn't sound like that bad of a waiting period for such a negligible outlay. The flash sale ends tomorrow, June 29, so it might be worthwhile to break out the credit card sooner rather than later.
There is a catch to all of this travel-related bliss, however. The cheapest fares are only redeemable for United's Basic Economy option, which only permits one small carry-on item, doesn't allow you to pick a seat, and forbids flight changes and refunds, among various other headaches.
Don't despair though: All of the flights included in the sale are relatively short, so checking a bag might suffice as a necessary trade-off. Besides, a slew of Standard Economy fares are still available for comparably cheap rates, which you can view here.