how can i load timed blocks simultaneously?

Hi there, so I have 2x carousels on my homepage. One of them is staggered to switch the image every 3 seconds, the other carousel is staggered to switch images every 9 seconds and the purpose of that is so that i have 3 images show next to the second carrousel before they switch to the next set of three. The problem i'm having is that the timing gets thrown off just slightly every now and again, and I can't figure out if it's because the images load at different times on the page or if it's something else. Any help would be greatly appreciated