Average time in seconds

It would be a conversion to DateTime with str_to_date , then # for an integer value and a division by 2 that would be the average of the result:

SELECT dtEnd, dtEnd, 
       ((UNIX_TIMESTAMP(dtEnd) - UNIX_TIMESTAMP(dtBegin)) / 2) media
from tempo tempo

The average in this case has its output in seconds like 30 seconds, 19 seconds, and so on.

References:

• 13.7 Date and Time Functions
• 12.3.7 Conversion Between Date and Time Types
• UNIX_TIMESTAMP () function
• UNIX_TIMESTAMP (), UNIX_TIMESTAMP (date)

Use the FROM_UNIXTIME function to convert to date and to make a difference to the TIMESTAMPDIFF function.

SELECT 
DtBegin,
DtEnd,
TIMESTAMPDIFF(SECOND,FROM_UNIXTIME(DtBegin),FROM_UNIXTIME(DtEnd)) AS TempoSegundos
from Interaction

SQLFIDDLE

Friend! You are not able to use TIMESTAM because your data type is DATETIME . That is, your query is looking for one type of data being in the database is another.