They've got about a billion years to cover... they won't run out of eras.
5 seconds sound clip from the X Minus 1 - A Gun for Dinosaur by L. Sprague de Camp classic radio drama series.
You can hear this line at 00:09:27 in the radio play.
Quote context
[...]
- Well, the machine won't work more recently than a hundred thousand years ago.
- Why? Well, I... Look, I'm no four-dimensional expert on the subject...
- And there's also some kind of taboo about sending people back to the same time again.
- Eh, it's paradoxes... mustn't have 'em.
- I'm not sure but the university isn't taking chances.
- They've got about a billion years to cover... they won't run out of eras.
- Hallo! Here we go! Now, cheers, eh?
- Well, that's done it. April twenty-fourth, eighty-five million years B.C.
- Now, then, careful. Keep the safety on your gun. And don't shoot unless I give the word.
- Why? Why should we have to wait for you?
- Because I'm responsible for everything you do. Especially if something goes wrong.
- I say, Raja, open the door, will ya?
[...]