Cannot find any mention of it in heroku docs. Am considering creating a history table and would like to know. As outlined here: https://github.com/arkhipov/temporal_tables and here http://clarkdave.net/2015/02/historical-records-with-postgresql-and-temporal-tables-and-sql-2011/
From what I can see, Heroku's Postgres service doesn't include that specific extension:
SELECT * FROM pg_available_extensions WHERE name LIKE '%temporal%';
...
(0 rows)
For posterity, here's the full list of available extensions (as of 2015/07/20):
SELECT * FROM pg_available_extensions;
name | default_version | installed_version | comment
------------------------+-----------------+-------------------+----------------------------------------------------------------------
dblink | 1.1 | [null] | connect to other PostgreSQL databases from within a database
tablefunc | 1.0 | [null] | functions that manipulate whole tables, including crosstab
hstore | 1.3 | [null] | data type for storing sets of (key, value) pairs
intarray | 1.0 | [null] | functions, operators, and index support for 1-D arrays of integers
pg_trgm | 1.1 | [null] | text similarity measurement and index searching based on trigrams
postgis | 2.1.7 | [null] | PostGIS geometry, geography, and raster spatial types and functions
pg_stat_statements | 1.2 | [null] | track execution statistics of all SQL statements executed
test_parser | 1.0 | [null] | example of a custom parser for full-text search
dict_xsyn | 1.0 | [null] | text search dictionary template for extended synonym processing
insert_username | 1.0 | [null] | functions for tracking who changed a table
pg_freespacemap | 1.0 | [null] | examine the free space map (FSM)
ltree | 1.0 | [null] | data type for hierarchical tree-like structures
test_shm_mq | 1.0 | [null] | Test code for shared memory message queues
adminpack | 1.0 | [null] | administrative functions for PostgreSQL
plpgsql | 1.0 | 1.0 | PL/pgSQL procedural language
plv8 | 1.4.2 | [null] | PL/JavaScript (v8) trusted procedural language
dict_int | 1.0 | [null] | text search dictionary template for integers
fuzzystrmatch | 1.0 | [null] | determine similarities and distance between strings
tcn | 1.0 | [null] | Triggered change notifications
sslinfo | 1.0 | [null] | information about SSL certificates
lo | 1.0 | [null] | Large Object maintenance
cube | 1.0 | [null] | data type for multidimensional cubes
tsearch2 | 1.0 | [null] | compatibility package for pre-8.3 text search functions
timetravel | 1.0 | [null] | functions for implementing time travel
redis_fdw | 1.0 | [null] | Foreign data wrapper for querying a Redis server
pgstattuple | 1.2 | [null] | show tuple-level statistics
earthdistance | 1.0 | [null] | calculate great-circle distances on the surface of the Earth
chkpass | 1.0 | [null] | data type for auto-encrypted passwords
refint | 1.0 | [null] | functions for implementing referential integrity (obsolete)
moddatetime | 1.0 | [null] | functions for tracking last modification time
seg | 1.0 | [null] | data type for representing line segments or floating-point intervals
pageinspect | 1.2 | [null] | inspect the contents of database pages at a low level
citext | 1.0 | [null] | data type for case-insensitive character strings
autoinc | 1.0 | [null] | functions for autoincrementing fields
pg_prewarm | 1.0 | [null] | prewarm relation data
isn | 1.0 | [null] | data types for international product numbering standards
postgis_topology | 2.1.7 | [null] | PostGIS topology spatial types and functions
xml2 | 1.0 | [null] | XPath querying and XSLT
postgres_fdw | 1.0 | [null] | foreign-data wrapper for remote PostgreSQL servers
postgis_tiger_geocoder | 2.1.7 | [null] | PostGIS tiger geocoder and reverse geocoder
unaccent | 1.0 | [null] | text search dictionary that removes accents
pg_buffercache | 1.0 | [null] | examine the shared buffer cache
uuid-ossp | 1.0 | 1.0 | generate universally unique identifiers (UUIDs)
file_fdw | 1.0 | [null] | foreign-data wrapper for flat file access
pg_logfebe | 1.0 | [null] | log via febe framing protocol to a unix socket
btree_gist | 1.0 | [null] | support for indexing common datatypes in GiST
pgcrypto | 1.1 | [null] | cryptographic functions
intagg | 1.0 | [null] | integer aggregator and enumerator (obsolete)
pgrowlocks | 1.1 | [null] | show row-level locking information
btree_gin | 1.0 | [null] | support for indexing common datatypes in GIN
worker_spi | 1.0 | [null] | Sample background worker
Amazon's RDS also doesn't appear to include it.
Not wholly surprising though: it's an interesting extension but unlikely to be requested often (since the functionality can be replicated indirectly).