How long does it take to make somebody a dependent?

How can I make my parent a dependent?
To seek dependent status for an adult family member, such as a father, mother, father-in-law, mother-
in-law, stepparent, or someone in loco parentis, DFAS will apply a financial test to determine
whether the family member receives over half of his/her income from the Servicemember. You must
submit the Servicemember’s or spouse’s birth certificate and proof of the relationship, DD Forms
137-3 and 1172 to show financial dependency, and proof of the family member’s identity to DFAS.
For someone loco parentis, this will include affidavits that that person stood in a parental capacity for
at least five years prior to the Servicemember (or spouse’s) 21st birthday.
https://www.dfas.mil/dfas/militarymembers/SecondaryDependency/SDC/SDC_FAQ.html

It's called "Secondary Dependency" or "Non-primary Dependents" for parent, parent-in-law, step-parent, parent by adoption, or any person who stood 'in-loco parentis' (in the place of a parent) to you for at least five years prior to your emancipation. Also, unmarried children ages 21 and 22 who are enrolled in an accredited institution of higher education on a full-time basis. Your primary dependent(s) is (are) your spouse or/and children.
How long does it take to make somebody a dependent?
Well, Time is not a factor here. There is no waiting period to submit a new claim. It also depends if your claim is approved or disapproved... and, if action(s) not needed for correction. However, you should receive a determination within 30-45 business days.
To qualify as a secondary dependent, the individual’s income, not including your contribution, must be less than one-half of the actual living expenses.
If your brother or yourself is ready to submit the initial application or redetermination package, make sure your brother contact DFAS office at 1-888-DFAS 411 (332-7411), option 4, then option 2. Nonetheless, y'all can submit complete application packages via the secure AskDFAS link: https://corpweb1.dfas.mil/askDFAS/custMain.action?mid=5340.

She will need to be dependent on him something to the tune of 75% or more, potentially lots of dollars, and not always what it sounds cracked up to be.