It's ok to flush anytime to get rid of excess salts and nutes, me I flush every 2 weeks or so, but not on a schedule at this point. I do flush when I switch the lights, followed by a 1/2 strendth dosage of Tiger Bloom on the first watering with Tiger Bloom.
Myflowering I go 4 tbs of Big Bloom and 4tsp of Tiger Bloom.
First week of flowering and last week before I flush I use 4tbs Big Bloom and 2tsp of Tiger Bloom, my logic behind the first watering is not over doing the nutes too early and the reason I go light before flush is so there is less to flush out..
Nico from HT magazine has a 3 day watering system which is: Water with nutes on day 1, Water with ph'd water day 2, no water day 3.