Google Maps allows riders to search for Trips up to 60 days into the future when the GTFS includes service through that period. This is particularly helpful for future Schedule Changes and Holiday Exceptions.
Note: Google Maps considers Trips involving more than one agency only up to 30 days into the future when calculating connections.
This is one reason to ensure your GTFS contains service at least 2 months in advance at all times. Some applications will consider a feed still 'valid' even if there is no more service according to the calendars, but it is still important to ensure that a feed does not expire. Some applications, like Transit App, will only consider a feed 'valid' through the feed_end_date (what is requested when you submit an export request.)