Unison: set times to true (if you want)
I’ve been using Unison for a few years now, so I’m ashamed to admit I only just noticed it wasn’t syncing the date modified attribute. This is because I’ve always worked with my desktop as a central repository, which kept the dates. My other computers have been mostly used for data duplication for increased data security. The much smaller number of files I changed on those other computers obviously came with recent filestamps, so that the problem didn’t stand out.
There’s a -times command-line option, but for something I always want that’s a bit inconvenient. Luckily you can change the same setting through the GUI, or you can add times = true to your profile manually. If my central HDD were ever to die suddenly, I’m sure I’d be glad I kept the last modified times.