Its a hormonal signal you are looking for in order to flower. Unbalancing phytochrome red and far red, during day the plant produces far red. During night far red becomes red, the plant will flower when not enough far red is produced. This is achieved reducing hours of light. But sometimes far red is accumulated and hard to get rid off. Other times not all the plant enters flowering at the same. 30+ hours of darkness just makes sure all far red has becamed red. This produce a little shock. But its not significant and will not stun the plant. Making a solid switch to start flowering