No....you can grow plants at almost any light cycle you choose but also not exactly sure why you are asking. I know it sounds crazy to manipulate the light cycles but there is a way to reduce stretching during transition to bloom phase if in fact that is your goal. Reducing daylight gradually also makes for an opportunity to increase bud mass.
The sun doesn’t flip from 18/6 to 12/12; it happens gradually over the summer forming big spires of cola bud outdoors. This is why people get stretchy plants with long lengths of bare stems indoors. First veg the plants at 18/6 until slightly smaller than the actual size you want to flower them. Then simulate the suns natural cycle by gradually reducing daylight by say an hour per week. Once you hit 14/9 most strains begin to throw pistils. At this point you can identify the sex and cull the males. I do this because once they are sexed you can re-veg aka monster crop the girls until they are of desired size and then flip to the final bloom phase. Makes for bushy plants with huge buds if it’s done right.