The transition should take place when hovering over #box_1
instead:
Remove the transition from .object1
and add it to the selector #box_1:hover .move-down
#box_1:hover .move-down {
transform: translate(0, 150px);
-webkit-transform: translate(0, 150px);
-o-transform: translate(0, 150px);
-moz-transform: translate(0, 150px);
transition: all 5s ease-in;
-webkit-transition: all 5s ease-in-out;
-moz-transition: all 5s ease-in-out;
-o-transition: all 5s ease-in-out;
}