Question 2 Interval and timestamptz

[Shawn <postgres(at)xmtservices(dot)net>]

Hello!

The second part of my question is:

Given a value as an interval, see previous posting, is there a simply method 
to take a given timestamptz value and a given interval value and create the 
sum or difference of the 2 in timestamptz format?

The scenario is that the afore mentioned tables, see previous post, in 
addition to the duration varchar field, also have a field called event_at_utc 
which is a timestamptz type.  I need to calculate the end time of the event 
given the interval calculated from the duration (varchar) field.

Any all all help is greatly appreciated.

Shawn