There are simply too many examples of people not following directions for auditions. If you are told to call on a specific day and time, call at that time. Some people thinks it makes them seem pro active if they call a day early. You don't make any friends by interrupting what people are doing by not following directions concerning when to call.
If the directions are to send an MP3 audition file with 3 takes, do not send 5
Production of voiceovers, video and all media requires a great deal of coordination. Make sure you help these people learn that you could be an asset in their hectic lives by following directions .