Feeding toms, when has the first truss set?

I hear that Toms should be fed once the first truss has set.
But here is where I am: I have 3 plants, all in one growbag (not great I know, but I'll learn!) all are in flower, and on the biggest plant (Ailsa Craig) I have my first 2 toms on the lowest truss.... about the size of marbles.
Is now the time to start feeding with tomatorite? Or is it too early for the other plants which are still only in flower?
I see "Once the first truss has set" a lot, but I'm not sure I understand it very well. All flowers turned to fruit? Should I maybe wait until all plants are showing fruit?

Thanks!

 

"I have my first 2 toms on the lowest truss.... about the size of marbles.
Is now the time to start feeding with tomatorite?"

Yes!

Don't worry that some of the other plants aren't quite there yet, there is nothing wrong in feeding a bit early, just that the general approach is to try to "stress" the plants a bit to encourage them to flower and set fruit.

When the first flower drops off and you can see the first "pin head sized" tomato replace the flower, then that has "set". Clearly the last flower on the bottom of the truss won't have even formed at that time, let alone opened!, so now you mention it "When the first truss sets" (which is a phrase I have always used) I now realise that it is a pretty meaningless, and imprecise, phrase in and of itself :thumb:

 

Not pedantic at all, being a Byslexic Dastard :D I can never see small errors like that, and I'd prefer the post was correct for whomever comes along next. Thanks for pointing out (and don't be shy in future!)

 

Question answered, many thanks!