There is a very sought after trait most chiefs and sheriffs desire in future employees: punctuality. If the deadline is a certain date and time, make a note to yourself to get there a day or so before. No civil service commission wants to hear that you got stopped for a traffic accident or bad weather. This is much akin to the "dog ate my homework" excuse. In other words, it will fall on deaf ears.
Another version of this reverts back to a prior point made - Incomplete applications! If it has to be held for a copy of a diploma for instance, the copy most often must be received before the deadline. Rules vary, but this is a fine print one here. If all else fails, recall what my sainted Irish mother says: "It is better to be an hour early than a minute late." Punctuality pays off; it could get you the job because someone else is slow.
Some of these points may seem incomprehensible to you, but my loyal assistant has seen each of these many times over. The point here is that this is your first opportunity to make a favorable first impression.
One additional point. Remember, you never know who you are talking to in this process. One agency I visited has its recruiting staff perform the background checks on all job applicants. As the recruiter told me, some applicants make unfavorable impressions with the wrong people. They must be cognizant of who they are in the presence of.
If you call my office looking for a job, keep in mind that my executive assistant is also the civil service secretary, so be nice to Michelle.