val startHour = SimpleDateFormat("HH:mm").format(pickup.begin())
The pickup.begin value is "Wed Apr 10 10:00:00 GMT+03:00 2019", so I need the start hour to be 10:00 +3h -> 13:00, but I get startHour value of 10:00.
I don't know how to add the GMT value to hour.
No, you’ve misunderstood. Wed Apr 10 10:00:00 GMT+03:00 2019 is (the textual representation of) a java.util.Date the value of which equals 2019-04-10T07:00 UTC. It seems your default time zone is GMT+03:00, and Date is trying to be friendly to you and print the time in this time zone, which is why it prints 10:00:00. 13:00 would certainly be incorrect no matter if you wanted the time in UTC or in your own default time zone.
The Date class returned from pickup.begin() is poorly designed and long outdated, so you may want to consider if a type from java.time, the modern Java date and time API, could be returned instead. It may also make the matter clearer.
Alternatively, convert that java.util.Date object to its modern counterpart, a java.time.Instant. Look for new conversion methods added to the old classes.
Instant instant = pickup.begin().toInstant() ; // Converting legacy `Date` object to modern `Instant` object.
Search Stack Overflow and read the Oracle Tutorial to learn more about Instant, OffsetDateTime, and ZonedDateTime classes.
You can use java.time on older Android versions if you add ThreeTenABP to your Android project. It’s the Android adaptation of the backport of java.time.
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