blitz: Clean up Timestamp and use joda Instant

Don't construct Timestamp using java.sql.Date or java.util.Date classes;
instead, use Instant to ensure it's in UTC.  The existing uses of these
classes was solely to get the time in milliseconds, which is the main
purpose of joda Instant.
Merge pull request #1382 from rleigh-dundee/timestamp-cleanup

blitz: Clean up Timestamp and use joda Instant