a good grower could get more than 500 grams from a 600w.
1 sativa could take up to 17 weeks to flower.
25 short flowering indicas could be ready in 7 weeks.
other than that, there is no truth.
it doesnt matter how many plants you have, they wont be done untill they are done. and different strains grown at the same time doesnt mean they will all be done the same time.