Some strains can start to flower even with 16/8 lights, but those are not normal strains. I surpriced that WW would start to flower with 14.5 lights, but i could see that happen.
I would say up it to 20 hours of light or maybe even 24 hours of light for a while. Darkness is what triggers the hormones that cause the plant to flower, you want to give it minium amount of darkness now until it goes into vegging and then turn back to 18/6 until you want to flower it. No point of trying to mess with weird amounts of light like 16 hours, that would likely just confuse the plant even more and continue the flowering in some half assed way and maybe cause it to hermie in worst scenario.