Even when they say "7 weeks" that may only be 10% of the outcomes.. maybe even less depending on the integrty of that particular breeder. It is not unusual to over-promise and under-deliver in this industry.. it's more of a standard than an exception to the rule.
Just as a breeder may claim it is 'purple' but only a small fraction will display the trait. The mere possibility allows them to rationalize the marketing strategy.
I've had a green poison fast F1 from sweet seeds. Took the normal amount of time. nothing fast about it. This is a gimmick. If something is 'faster' it probably also correlated to smaller yield. Without anany info comparing grams per sq ft per time invested, no way to know if it is a positive or negative trait. Just unverified conjecture as always.
growth rates do vary, so if you account for that, 'faster' just means smaller. Can't circumvent the range of potential rates of growth. can only take in co2 so fast.. can only use it so fast... some plants are more efficient than others in this regard, but there's still a ceiling on it.
The plant isn't engaging in quantum growth :P where some portion develops in a pocket univvers and poofs into existence!
:)