Regardless of the time of day you decide to fly, the ticket price will remain around the same. Book flights from Johannesburg to Dayton as you normally would.
This flight path from Johannesburg OR Tambo to Dayton was viewed by 177 users in the past month. Keep an eye out for changes in search interest prior to high and low season.
When travelling, it's generally smart to pack in preparation for rain or any other conditions that may arise. The rainfall in Johannesburg is roughly similar to Dayton. You can assume this to be the case over the next 15 days.
Temperatures around the 29 °Cs can be experienced in July. The weather in Dayton is hotter than in Johannesburg. Plan for potential changes in flight availability as peak weather approaches in this location.