What week to Flush

What week would you start flushing? beginning of week 7 or 8?

I flush the last 2 weeks of flowering. As to what week, that depends on the strain and how long it needs to flower.

2 weeks before you plan to harvest

.....yeah. i go with two weeks before harvest... i also flush about once a month all during all stages of growth just to wash out any built up salts in the soil...