NOT an expert, but I think the only temperature that generally matters on earthworks is below freezing.
It is much more work for the construction equipment to scrape up or breakout frozen ground. However, it can be done with enough HP.
I do not imagine there is any possible way to perform compaction on frozen ground, or in a core trench fill that contains chunks of frozen material.
It is usually a big advantage to perform heavy construction work when your site is dry. If fall is a low precipitation time in your area, then that might be an excellent time to schedule your project. Definitely give yourself a cushion before the hard freezes start. However, IMO an early, light snowfall event is not going to disrupt your job.
