Redmine

so I wanted to add a bunch of related tasks.. basically a template for a fda regulated validation project. I was going to add a start date and an end date for the first task.. have the next follow it.. which sets the start date automagically.. but how do I say the next one last 2 days other than setting the due date? (in order to set the due date of 2 days after start I need to have the start date.. which sort of defeats the purpose of having the relationship establish the start date for me.. but to do that I need to save it and the relationship first. .I'd hate to have to go back and update/save it again. . setting the estimate of 16 hours doesn't have any effect on the due date.. (nor the Gantt chart.. nor the planning plugin etc..).. I just want to say this one follows that one and is 3 days long. etc .

thanks!