You may have your new starter students come in for a trial period, open day, or introductory period (sometimes called a 'transition' period or week). You may want to have them feed into an API connection, take payments, take registers and create a timetable for these joiners.
We wouldn't recommend adding these students to Arbor.
This is because to enable you to take payments or registers, you would need to enrol them into your school. This means they would no longer be applicants, but current students at your school.
This will then be incorrect for the School Census, as students will be enrolled full time in two schools at once.