Ive messed up my dark periods plenty of times throughout flower. You might be ok but that really depends on a strains tendency to hermi from undergoing too much stress.
Usually a little light during the dark period during flower is ok, and if you ran the lights for 18/6 then stepped down 2 hours to 16/8 for 2 weeks instead of one you should be fine. All that really means to me, as far as I know, is that you just had a short day veg cycle. Most plants won't even start flowering until you hit 14 hours or less of light per day. Flowering is triggered when a buildup of hormones reach a certain level. The hormone is only produced when the plant is in darkness, it takes a good week for the plant to really switch to flower mode. So your plants just got a week of less dli than an normal 18 hour day. Think of it as a cloudy week outside. Just go to 12/12 I'm 99% sure you're gonna be fine