Usually the form will require a signature by a club officer or your test chairman to attest to your eligibility. Sometimes they require a signature from your pro to attest to your readiness. Usually, you will get a mailing from the host club about 10-14 days before the competition. This mailing will list your event day and times, and will provide a map to the rink, parking instructions, and other necessary information. In general, it won't help to call earlier than that, since they can't make up a firm schedule until they have all the entries and go through a huge scheduling effort to make it all work.
Most competitions run over a weekend.
But because of the number of entries that most get, many have to start before Saturday. Sometimes Friday, once in a while Thursday too. You will compete against other skaters of approximately similar experience. You may or may not be competing against skaters of similar age. The basic separation is by test level.