Add extra hours to timestamp columns in Pyspark data frame

One approach, that doesn't require explicit casting and uses Spark interval literals (with arguable readability advantages):

df = df.withColumn('testing_time', df.testing_time + F.expr('INTERVAL 2 HOURS'))
df.show()
+---+-------------------+---------+
| id|       testing_time|test_name|
+---+-------------------+---------+
|  1|2017-03-12 05:19:58|  Raising|
|  2|2017-03-12 05:21:30| sleeping|
|  3|2017-03-12 05:29:40|  walking|
|  4|2017-03-12 05:31:23|  talking|
|  5|2017-03-12 06:19:47|   eating|
|  6|2017-03-12 06:33:51|  working|
+---+-------------------+---------+

Or, in full:

import pyspark.sql.functions as F
from datetime import datetime

data = [
  (1, datetime(2017, 3, 12, 3, 19, 58), 'Raising'),
  (2, datetime(2017, 3, 12, 3, 21, 30), 'sleeping'),
  (3, datetime(2017, 3, 12, 3, 29, 40), 'walking'),
  (4, datetime(2017, 3, 12, 3, 31, 23), 'talking'),
  (5, datetime(2017, 3, 12, 4, 19, 47), 'eating'),
  (6, datetime(2017, 3, 12, 4, 33, 51), 'working'),
]

df = sqlContext.createDataFrame(data, ['id', 'testing_time', 'test_name'])
df = df.withColumn('testing_time', df.testing_time + F.expr('INTERVAL 2 HOURS'))
df.show()
+---+-------------------+---------+
| id|       testing_time|test_name|
+---+-------------------+---------+
|  1|2017-03-12 05:19:58|  Raising|
|  2|2017-03-12 05:21:30| sleeping|
|  3|2017-03-12 05:29:40|  walking|
|  4|2017-03-12 05:31:23|  talking|
|  5|2017-03-12 06:19:47|   eating|
|  6|2017-03-12 06:33:51|  working|
+---+-------------------+---------+

Based on @Psidom answer,

Since that in my case the column testing_base has quite changeling time-format, instead of using in my case F.unix_timestamp("testing_time", "yyyy-MM-dd'T'HH:mm:ss.SSS'Z'") which works for records with milliseconds but returns null for records with seconds granularity... I handled it in this way:

import pyspark.sql.functions as F

df.withColumn("testing_time", 
    (F.unix_timestamp(F.col("testing_time").cast("timestamp")) + 7200).cast('timestamp'))

In this way whatever the time-format is for the field testing_time, it is handled by the cast function provided by Pyspark.

You can convert testing_time column to bigint in seconds using unix_timestamp function, add 2 hours (7200 s) and then cast the result back to timestamp:

import pyspark.sql.functions as F

df.withColumn("testing_time", (F.unix_timestamp("testing_time") + 7200).cast('timestamp')).show()
+---+-------------------+---------+
| id|       testing_time|test_name|
+---+-------------------+---------+
|  1|2017-03-12 05:19:58|  Raising|
|  2|2017-03-12 05:21:30| sleeping|
|  3|2017-03-12 05:29:40|  walking|
|  4|2017-03-12 05:31:23|  talking|
|  5|2017-03-12 06:19:47|   eating|
|  6|2017-03-12 06:33:51|  working|
+---+-------------------+---------+