At TechShop, laser cutter time is limited to two hours. I try to not be a jerk and have my area vacated before that deadline. But this is a big job.
I figured out a technique to estimate the time it takes to etch the board today. Basically, I let the etch run for a little while, and measure the time taken. The time taken is roughly determined by the area covered. So, chop the whole image into a few rectangles, find the ratio of the area of those rectangles to the first rectangle, and multiply by that first measured time.
Today's etch pushed me 5 minutes into overtime, but luckily nobody showed up after me, so I didn't have to beg forgiveness.