There does not seem to be a way to subtract from a date in qSIChartView, only Add.
In the help document for Complex Filter:
Date function — The following date functions are supported: AddSeconds, AddMinutes, AddHours, AddDays, AddMonths and AddYears. Their syntax is DateFunction(dateValue, number). For example: AddDays([TODAY], 7) adds 7 days to today's date.
How to use subtract function on Complex Filter for qSIChartView on dates?