Depends on your lights and how much they can deliver the needed photons to feed the plant with the needed Daily Light Integral.
With powerful lights that deliver the needed PPFD for flowering of between 500 and 800 PPFD without using supplemental C02 you’ll want to calculate your DLI and see how many hours you should keep lights on in order to get the most growth from your ladies with the light/s you have.
Using the less expensive LUX meter and using their conversion calculator you can determine what your PPFD is and then calculate your DLI based on stage of growth.
Example:
HLG 260XL fixture with a reading of 40,000 lux (using lux meter or I also hear they have phone apps) is equivalent to 583 PPFD
583 x 3600 (seconds in an hour) = 2,098,800 then multiply that by the number of hours your light is on (say 12 hours) = 25,185,600 then divide this by 1,000,000 (or just move the decimal point over 6 places) and you get a DLI of 25.1856
If your target DLI is say 40 per day than you’ll either need to move lights closer to plants (increases your LUX and in turn the PPFD) or increase the hours they are on Per day or get better lights that can reach the needed PPFD.
Here are some charts and some links to help better explain this stuff as there is a lot but once you’ve looked through things it becomes clearer.
This may be more than you wanted but if you’ll be doing this for a while it will be something you’ll eventually want to understand.
I just went through the process of figuring out how long to have my lights on in my Auto grow tent as well as my Photo grow tent.
Hope this helps