function WeekSpan(const ANow: TDateTime; const AThen: TDateTime): Double;
double __fastcall WeekSpan(System::TDateTime ANow, System::TDateTime AThen);
Returns the number of weeks (including fractional weeks) between two specified TDateTime values.
Call WeekSpan to obtain the difference, in weeks, between two TDateTime values. Unlike the WeeksBetween function, which only counts whole weeks, WeekSpan reports incomplete weeks as a fraction of an entire week.