A film described as a Friday release is usually already playing on Thursday evening. The schedule exists because of how opening weekends are counted and how cinema capacity behaves during the week.
The opening weekend is the number that travels
Box office reporting is built around the first three days, and that figure is what gets published, compared and used to judge a release.
Thursday preview takings are folded into the Friday total, so they raise the reported weekend rather than sitting outside it.
Every ticket sold on Thursday night therefore counts twice over, once as revenue and once as evidence of a strong start.
Thursday capacity is otherwise wasted
A cinema's costs are largely fixed once it is open. Staff, projection and the building are paid for whether the seats are filled or not.
Thursday evenings are historically weak, so adding a high-demand title costs the exhibitor almost nothing in displaced business.
The audience most likely to attend is also the one most willing to move a night earlier to be first.
Marketing spend has a fixed finish line
Campaigns are built to peak in the days before release, and that spend cannot be usefully extended once the film is out.
Opening a night earlier converts the final surge of advertising into ticket sales while it is still at maximum intensity.
It also front-loads the audience that is least dependent on reviews, which matters when critical reception is uncertain.
Early screenings seed the reaction cycle
Audience reaction now spreads within hours of the first public showing, and that reaction shapes Friday and Saturday attendance more than any advertisement does.
A Thursday opening gives a well-received film a full news cycle of enthusiasm before the main weekend begins.
It also means a poorly received one is known to be poorly received before most tickets are bought, which is a risk distributors accept in exchange for the upside.
Start times crept steadily earlier
Previews once began around midnight, which technically fell on release day. Competitive pressure pulled them into the early evening and then into the afternoon.
Each distributor that moved earlier gained a few hours of exclusive attention, and the rest followed rather than concede the head start.
The practical limit is the point where a Thursday screening starts cannibalising Friday rather than adding to it, and major releases now sit close to that line.
Smaller titles often skip previews entirely, because their audience arrives on recommendation over the following weeks rather than on the first night.