Once a tomato plant is mature it will start to flower so keep it on the same light cycle.

i thought we need to slow down the light cycle from 18 hours to 12 hours once the flowering takes place

are you sure ?

Does anyone have more info on this one - what is up with the 18/6 vs. 12/12 light cycles and fruiting crops?

Some plants are triggered by photoperiod (daylight vs. hours of darkness) to flower and/or fruit. Tomatoes as with most other garden vegetables are not one of them and can be kept on the same light cycle.

I have had my Oregon Spring Bush tomatoes under 17 hours of hps light since first set of true leaves. They are flowering just fine.

Cool, thanks! I'll keep this in mind.

So the longer you run the lights the more fruit you get? How much night do tomatos need - is 18/6 still a good cycle or does anyone recommend something else.

I am using T5 HO - two grow and two bloom bulbs.

Ive always grown under 15hours of HPS light start to finish without issues. Some plants DO require flower of 12/12 though.
Tomato just isnt one of them.