When you go to strengthen skills (a unit or all skills), you will get the choice between timed and untimed practice. My Duo is set to Spanish right now so I can't check for English, but I think the options are called "untimed" and "against the clock" or something like that.
Glad to help. PS if you click "reply" directly under the comment, the person will get a notification. For longer conversations it is helpful because the responses all "nest." (See a post with lots of comments for an example.)