Two diamonds begin a free fall from rest from the same height, 1 s apart. How long after the first diamond begins to fall will the two diamonds be 10 m apart?

Question

The part that confuses me is when the diamonds are 1s apart.

s=(-1/2)g*t^2
At t=1sec the first one has fallen 4.9m and the diamods are only 4.9m apart. At t=2sec the first one has fallen 19.6m and the second has fall 4.9m and they are 14.7m apart. Thus your time should be between 1 and 2 seconds, right? Now try to work it.