Also, if giving a bunch of extra hours of light, and then taking away that extra light will certainly cause flowering-whether you intended it or not.
This depends on the plant. Many don't care at all, they reach a certain age/size and they flower, regardless of the # of hrs of light (day-neutral - ie. tomatoes, soybeans) If given less than ideal light, they will still flower, it just will take them longer to get big enough to flower.
Other plants have a strict requirement for short nights. Many of these plant will NEVER flower, no matter how big or old they are until they receive a short enough night. These plant will still flower under 24 hrs of light. The important flowering time keeper in plants (phytochrome) gets converted to the active form by red light during the day, and slowly spontaneously converts to the inactive form at night. By measure the ratio of these two forms, the plant knows when to flower. This is how the flowering clock works. They have other clocks for other things. Short night plants (like hops) need low levels of the inactive form to flower.
The other class is the long day plants (poinsettias, Xmas cactus). These plants will never flower no matter how big or old they are until they receive a long enough night time. These plants need to have lots of the inactive form present first thing in the morning to flower. If you grow these under long days, dropping the light still might not get then to flower, even with a 6 hr change. You must get below the critical limt for them to flower (it varies from plant to plant).
Now if you can get yourself ahold of a good far-red (690 nm) light source, with no red light (660) you can cheat for long night plants. Besides slowly converting to the inactive for at night, you can switch it very quickly by shining far-red light on the plants (avoiding any red which would defeat the purpose). In affect, one could artificially imitate a long night. In the past it was hard to find good filters that would block out just one or the other wavelength. Now there are LEDs available in those two specific wavelengths so one can really mess with plants.
I don't use lights on my hops. I use lights on my large houseplant collection