Sensi Seeds -Northern Lights ?

It's possible to get clones to root and flower at the same time. You can try this when you're very comfortable with cloning and have a normal success rate of 80-90%+. However, this is usually done to save some time when cloning for sex and quality selection, not for producing buds.

A clone flowered without roots can turn into a healthy specimen, which will give a good idea of the potential quality of the mother it was cut from, but it should not be expected to turn into a production plant. I doubt it would be practical to flower dozens of rootless clones and expect a worthwhile harvest from them.

Flowering when super-small also works much better with Sativa hybrids, as they will gain height all through the flowering stage. I have flowered Jack Herer (pheno A) as unrooted clones under 10cm tall, and they finished over 40cm, with properly developed buds.

Flowering a straight-Indica Northern Lights clone (as opposed to NL#5xHaze) at a height of 3in/7.5cm would probably result in a finished plant of around 6in/15cm. We usually expect Indicas to add between 50% and 100% to their preflowered height.

So if you're just interested in testing the quality of the mothers you have kept, and if you're good at making clones, flower tiny or unrooted clones by all means.

But if you're planning a proper crop from these Indica clones, you should let them grow larger before you flower them - at least 6in/15cm, which would allow them to finish around 12in/30cm.