GTFS routing api's departure time

I’m trying to use reader-gtfs to provide PT routing in my service. library is expecting Instant as departure time parameter. any advice how i can translate local (local as origin point’s local) date/time to Instant?

During gtfs file parsing, gtfs-reader is using zoneId given in files, and translating everything to Instant. As library user, i don’t really know which ZoneId will be used to serve request, so i don’t see what is proper way to translate date time to instant.