The absolute load shouldn't matter THAT much….in my experience the % is a better indicator of intensity.
I would recommend not doing them on Thursday. While I typically wouldn't use them in-season, on the rare occassions when I have, I've always had better success doing them no later than 3 days before a meet (Mon-Wed).
I use them as a means of developing strength by switching up the stimuli. I also use it as a lead-in to supra-maximal fast-eccentric work which I've found useful for enhancing leg stiffness.