I do this kind of thing all the time. It's a bit of a hack, but it works.
1) From the "y=" prompt, before you type in your equation, select the "{ x < 0, x = 0, x > 0" option (i.e. the piece-wise defined option) from the pull-down menu at the right-hand side of the input bar.
2) For the number of conditions, type "1" and click OK.
3) Enter the right side of your equation into the first blank.
4) In the second blank, enter your limits on t. You can't write "0 < t < 6", because Grapher can't understand that. Instead, you need to write
"(0 < t)&(t < 6)".
That'll do it. Your equation doesn't have an N in it, so that's why I didn't address that part of your question, but if the directions above work for you, you can probably figure out the rest on your own. Good luck!
