TL;DR - switch to 12/12, both will be fine :)
Have you seen the journal with the 200 day old autoflowering gelato..?
growdiaries.com/diaries/124111-grow-journal-by-dingle-dangle
haha :p
I'm new to autoflowering plants, but I've seen some big variation in the strains that are growing when it comes to flowering.
From only 3 weeks old to 8 weeks for the same strain, from the same batch!
It may be that your plant has a few genes that dictate flowering more dominant from its major strain more than c.ruderalis, or is heavy sativa (WCa is mostly indica though).
So, I guess the easy answer is - if you are becoming impatient, and don't want to grow it HUGE, to start it flowering now is:
0. Wait another week, if you can, since you have two at different stages under a single light
While there's no issue having the lights at 12/12 for both - you might want to continue the extra light to plump up the growth and buds a little for your other plant.
So this will be a trade-off-trade-off situation. Personally, I'd wait a few extra weeks and see what happens...
1. Ensure you are not disturbing the darkness, and that no more than a moon's worth of light is bleeding in
2. Mimic autumn conditions by lowering the temperature and humidity in the growspace - you can use more fans blowing with ventilation open, and turn the light cycle down to 12/12 (or even 10/14)
You might have hot lights or a warm space and a lot of humidity thanks to the flowering plant next door, and 12/12 will get the plants flowering as if they were photoperiod
If that doesn't work and, after a week, it is still not starting to show any hairs or balls:
4. Give it a dose of darkness for 24-48 hours. This is ok, and is something that you might do with photoperiod plants, anyway
This is a strong signal that the days are definitely becoming autumnal for long enough for it to start pushing them pistils, without stalling growth or being a detriment to the plant
It's something you might do also before cropping the plant, to aid in flushing chlorophyll and to force the plant to replenish the THC (which degrades a little in the light) and terpenes (which evaporate with transpiration)
5. Don't disturb the darkness, or allow more than a moon's worth to bleed in
Can't stress that enough