how long before i need to take out nutes???

I'm a newbie at this and I'm growing using hydroponic system and into my 5th week of flowering and I like to know when i should take out the nutes and add just water and after how long before i cut ?

start your "leech" (only water/no nutrients) on or around week 8. I think a week is more than enough time to leech your plants of nutrients. other variables will probably judge your cut time more so than the amount of leech time, but 8 to 9 weeks total in the flower stage is usually the ticket.