Ask the school for guidance first. If they want a package, do that as early as possible. Ask if there are implications for financial aid or support, by sending materials early, as there is at my institution. At KGI, priority round applicants are eligible for consideration for the full amount of fellowship support since none has been awarded at that time.
If they have no guidance or say, start sending materials as soon as possible so you have time to react if something doesn’t make it. Leave yourself a cushion of time to react and find a missing document if needed. It is ideal to have receipt confirmation for all your application materials before the deadline. Not having it can cause you a great deal of uncertainty during a stressful time.
Sending everything as a single package reduces costs and complexity because you ship less and have less to track. It is also appreciated by the admissions committee because they only have to open your file one time and can process everything at the same time.
What other factors do you consider when deciding when to send materials?