Thanks for the info about the checksum stuff. Universal patcher sounded easier though, so I went with that.
I set the new time to 1 second, out of concern that setting it zero might lead to an off-by-one error somewhere - it probably won't, but I'm paranoid. Today I tested it in the car, and it worked. I did a full flash to get the OS blocks with the parameter change and the checksum change, and then was able to do two test writes with only a 1-second wait.
I wish I'd figured this out sooner, there's been days where I did 5-6 flashes working on my idle, and each of those is a whole minute of my life that I won't get back.
Please don't PM me with technical questions - start a thread instead, and send me a link to it. That way I can answer in public, and help other people who have the same question. Thanks!