Shouldn't be an issue as the previous grower said, though also I can't see any reason to experiment like this, using timer socket is generally more straightforward. Oh, and you shouldn't do it in a way that it gets 12 hours of darkness in a row when still on vega, it could trigger flowering. I've read somewhere that light stress might turn her into a hermaphrodite though I've never had those problems. In general, plants listen to light change, they know when the autumn starts by the number of red lights at the dawn, etc... And living creatures in general like natural rhythms, even switching to 12/12 is considered a stressful change AFAIK.