A practical default is 15 to 25 minutes
That window gives you time to find each other, say hello, buy anything you need and locate the auditorium without standing around for an hour.
If the venue is particularly busy, the film is a major opening-weekend release or the cinema has a complicated layout, favour the earlier end.
Use a precise meeting point
A specific entrance, café or foyer is much more useful than a district or square. The goal is to remove ambiguity before either person leaves home.
Costar cinema guides include a recommended first-meeting point for each launch venue.
Do not rely on trailers as your buffer
Advertising and trailer lengths vary. The advertised screening time should be treated as the anchor for your plan, not an invitation to arrive late.
If the cinema has a strict late-admission policy or you are attending a special event, arrive earlier.
What if one person is late?
Send a simple update if you can. The other person should keep control of whether they wait or go into the film.
A first meeting should never require someone to miss the screening they wanted to see.