When you reveal a nav command do u have to declare if u are taking the token or using for a speed up/yaw click before you go on and attack? or is it a choice after you attack to bank the token or spend the command?

You Reveal your Dial.

With All Commands, you decide, right then and there:

1) I am keeping the Command Dial, in anticipation of Spending it this turn...

2) I am changing this Dial into a Token. Wether or not I spend that token this turn is still a Question.

...

So if you decide to not transfer to a Token, you might as well spend the Dial later in the turn, because otherwise its Gone

If, for example - as you asked - have a Nav Dial. You are deciding only if you are keeping the dial or getting a token, at that step. You decide to keep the Dial.

You then go and do your other Tokens, and your Shooting, and then you get to the Determine Course step.

NOW you decide if you want to Cash that Dial in for a Speed Change, A Yaw Increase, Both , or Neither ...

If you decide neither. The Dial disappears at the end of that step. You do not get a further opportunity to turn it into a Token for later. That step has passed.

Worth pointing out that a couple of the commands (squadron and engineering) are both resolved at the same time you decide whether to take a token or keep the dial. You can't reveal a squadron dial, decide to keep it, make your attacks with the ship, and then use the squadron dial.