When is the ideal time to start a “from scratch” backyard landscaping project in Houston?

Given the weather, when is the ideal time to start a project like this? I’ll be hiring someone to do it and have already gotten my bids. Just need to pull the trigger, but I don’t want to start too early while we still have near 100-degree temps.

Will be planting St Augustine sod, creating new flower beds, planting a few 15-gallon trees, some smaller 5-gallon plants, etc.