I had trouble understanding exactly what you want, but if you want the firebrick divs to wait 3 seconds until wheat is done AND you want the whole sequence to repeat you can use just 1 timeline.
tl1.staggerTo('.box1', 1.3, { ease: Elastic.easeOut, x: 200 }, 0.05)
.staggerTo('.box1', 1.3, { ease: Elastic.easeOut, x: 400 }, 0.05)
.staggerTo('.box2', 1.3, { ease: Elastic.easeOut, x: 200 }, 0.05, "+=3") //wait 3 seconds before box2 starts
.staggerTo('.box2', 1.3, { ease: Elastic.easeOut, x: 400 }, 0.05)
If you need something different please clarify the exact order things should happen and how the delays and repeats should work. I wasn't sure if the wheat should start repeating on its own before redbrick started.