Additional deflection beyond instantaneous deflection is known as "creep". The amount of total creep deflection of a structural member is dependent on the environment and loading conditions.
Although creep deflection sounds like a serious problem, it normally does not need to be accounted for because the applied loads are typically a fraction of the design loads.
Weyerhaeuser software (Forte® and Javelin®) does not account for creep. Refer to Technical Bulletin TB-101 for more information regarding creep and how to predict total creep deflection of a structural member.