m0useanswered grow question a year ago 13/12 is a total of 25hours. our common earth day is aorund 24hours.
All strains will flower if they have 12 hours of uninterrupted darkness when they are sexually mature.
a few strains will do it with 10 or 11 hrs even.
If you want to keep it in veg longer you need to ensure the Dark period does not last longer then 9hrs. I like a 18/6 for this.
Good Luck!