Dayparting
Restricting bids by local time of week. It lives on bid modifiers, counted in minutes, and is not in the targeting-key catalog.
Dayparting is bidding only in some hours of the viewer's week. It answers "what local time does the person see the ad," not "when does our money leave today."
On the exchange we buy through, dayparting is a bid-modifier term, not a targeting key. The targeting catalog has no clock. user_time_of_week is counted in minutes from Sunday midnight, 0 to 10079. A range of [9, 12] is three minutes, not 9 a.m. to noon. An hours-based implementation would compile, raise no error, and never deliver.
A modifier applies only where it matches. To suppress hours you list the hours to turn off (multiplier 0), not only the hours to allow. The viewer's timezone is what user_timezones is for. That smear across zones cannot replace a UTC budget stagger.
We claimed dayparting was absent because we looked at targeting keys only. That claim was wrong. The capability is verified on our exchange account and is not a one-click buyer control in the product yet.
Read dayparting is not on the targeting catalog. Do not confuse it with pacing.