Anytime you have a bad ph, nute problem, or they start to look bad, you can flush...all you are doing is leaching the toxic salt build-up away...you have to allow them to dry out well before re-adding nutes...In your case, fluhing under the lights might allow plant to perk up, meanwhile you are running clean ph'd water thru plant(some people like to run a 50% solution to plant after leaching)...

what kind of water do you use? sorry if I missed it.

If you have a nice amount to harvest and you are at least in week 6 of flowering, you will get some nice "up high" buddage, Imho.

But if they look nice after leaching, you might want to wait a couple. lw