There are two rules that exist with a link:
The default link rules are 100% complete and no delay. If Task 1 is linked to Task 2, the default rules specify that Task 1 must be 100% complete before Task 2 can start, and Task 2 can then start right away, with no delay.
To edit the rules for a link, select the link on the Whiteboard. The Data Panel shows the link rules:
The default link is a Finish-Start link. You can simulate a Start-Start link by entering 0 in the % completed field.
The delay in days must be a number >= 0.