28 days, too early to switch to 12/12

Hi all, got a first grow going it's been 29 days under a 400wt hps light at about a foot away getting plenty of water and veg nutes watering till 10% run off I just switched to 12/12 last night as I'm using a closet and they would roughly be a 3rd of desired height I haven't got stain names but these two plants the only two I have are different. Is this too early or to immature of the plants to force flowering now?
Also they are in coco coir.

HI BuckWheat, well as it is your first grow it is all a learning curve. 29 days sounds ok
but not all plants will stretch 3 times the size in flower sativas will but indica you would
be lucky if they stretch to 1 to 1.5 times just have fun and enjoy your grow.

Thanks for the info, yeah it's good fun kinda therapeutic in a way hehe.