Where is the Gantt Chart in DayBack?
The Gantt Chart is called "Horizon" view in DayBack and was added as an in-app update in December of 2015.
You'll find a nice introduction to the Gantt Chart, along with a movie of it in action there: Gantt Charts in DayBack Calendar
Alternatives to the Gantt Chart
In addition to the gantt chart there are a couple other capabilities that may help you look at your schedule across multiple days. DayBack has multi-day resources scheduling which lets people look for gaps across multiple dates (up to 14 days at a time):
The other feature that can help balance your workload is the "grid view" which is like a pivoted version of the multi-day resource view: