In English, there's a word that indicates the immediate past: just. If you want to say that you stopped talking about turtles very recently, you would say
I just talked about turtles.
You can't say I now talked about turtles, although I just now talked about turtles is fine.
There is no corresponding common word for the immediate future, so we use now combined with will or am going to instead. So if you want to say you will start talking about turtles very soon, you say
I will now talk about turtles.
The present tense constructions in English don't work for this:
I am now talking about turtles,
would imply that you have already started talking about turtles, and
I now talk about turtles,
would probably be interpreted as habitual—these days I tend to talk about turtles.