So yes, time yourself. Have a concise version of your answer - I'm not going to say a number of minutes, some answers are longer and some are shorter.
Some candidates type out their answers, so time yourself speaking one out loud, note the word count and edit your other answers to a similar length. Some people write long and then edit it back and that seems to work well for them. If your answers are too long, you will find that many public sector interviewers will cut across you to move you on.