One requirement of Transportable Tablespaces (and of course Full Transportable Export/Import as well) is to have identical database character sets AND identical time zone settings.
Problem
Source database has a lower time zone setting than the default target database in the destination home.
Lets assume you’d like to migrate an Oracle 11.2.0.4 off IBM AIX and migrate it into Oracle 12.1.0.2 on an Exadata meaning Oracle Linux 6. The source time zone version if it has never been upgraded would be TZ V14 – whereas the new Oracle 12.1.0.2 database you’d create would get TZ V18 by default.