Hi Bill,
The eSwitcher and the flight sim do not talk to each other. The eSwitcher simply changes RTMM's seasonal files to match the date chosen. Since FSX & P3D only change seasonal looks at month boundaries, you could set a date, e.g. July 7th, in eSwticher and then the sim will match for any date that is set in the sim as long as it is within the month of July.
Hope this helps.
Rod