Construction stage - post tensioned

Hi

I have a question. I need to input prestressing force after 10 days, so I get that I need to do a proper stage, when my PT0 loads starts. And then my force is going to decrease due to creep, relaxation and shrinkage.  Finally after 50 or 100 years i get my lower PT8. 

1. So i understand if i need to prestress after 10 days so I have to choose in creep properties of my element - age of concrete when loading started 10 days ? Or in other place ? 

2. Where can i find information what periof of long term losses are considered 50,100 or maybe other period ? 

3. How to submit presstressing forces in stages ? I need to add new loads after 10 days, and then how to remove it ? Or maybe forces decreases automatically ? 

Thanks for your help.

Barbara