Sometime during the bomb episode, this one.
Hours
They've been up there for hours. Hours and hours, Derek and Preston and Meredith and Cristina.
She can feel the tension, everyone waiting, waiting for something, anything. Eyes open, forced to see only for stability. So much depends on a potted plant. One sound, and the whole place could unravel.
And then it hits. She feels it a second before it actually hits, but it does, in her head, and she knows that something has blown up.
And it feels like hours before she sees Derek again.
Reference: "So much depends on a potted plant" is a riff on "So much depends on a wheelbarrow," a poem by William Carlos Williams. The idea is this: You're thinking about something, and you stare absentmindedly at an object because you're thinking so hard. For an instant, right before your eyes zone out, your entire life depends on that one object. For an instant, nothing else in the world matters, excapt that this object exists, and you're looking at it, and it's still there. So much depends on a potted plant.