Scheduled Departure and Arrival Date/Time

How early scheduled departure and arrival date/time can be available for specified flight no./date? i.e. how long before the actual departure of the flight?

typically flights will become visible with scheduled times when it is 24 to 48 hours prior to departure if it is a major airline that publishes their schedule in advance to us. if that is not the case, then it may only become visible when the flight plan is filed with the aviation authority, which may be less than 2 hours to departure.

Thanks for the feedback! Is there a smart way to setup our search engine to query on the scheduled departure and arrival time? We need to avoid high traffic on the server, so for example, are those major airlines and the other inconsistent ones predefined? And hence we can setup the query intervals according to them.

Any updates on my enquiry?