As far as I am able to understand the concept based on this early post over at Smogon, the initial seed for 3DS Pokemon games is calculated using 1) the number of CPU ticks that have elapsed since the CPU was powered on, and 2) the number of milliseconds since 00:00:00, 1 Jan 2000. Considering that the initial seed is basically the digest of SHA-256, is it practically impossible for any "Seed to Time" programs to exist? So even if we could somehow manipulate the message (inputs), it wouldn't be much use.
The above train of thought stemmed from wondering whether certain PID/EC/Nature/IV/Gender/Ability combinations are theoretically invalid given a specified met date of a Pokemon, or can every possible initial seed be obtained on any given date? I know in Gens 4 and 5, not every seed is available on every date (some aren't even valid seeds in Seed to Time). Also, unlike Gen 5, where a 64-bit seed is split in half and each 32-bit half can be independently advanced, calls in Gen 6/7 reroll the entire 64-bit value, and I assume (0x41C64E6D * Seed) + 0x6073 doesn't apply anymore.
When genning, I want to be as legal as possible (I know Nintendo doesn't care), which I believe involves using 3DSRNGTool to find a feasible frame with the desired spread and corresponding PID/EC combo.