This would be a direct deposit into the required accompanying checking account, correct ? I assume you already had or indeed did setup the NFCU checking account.
They say the DD must be “Net Pay” or “payroll allotment”. Net Pay is no good, as that’s a third-party DD service. An allotment is a portion of ones pay that a person in the military authorizes to be paid to someone else or an institution, so it wouldn’t need to represent an entire paycheck, just the part someone would be setting aside.
It really doesn’t matter what $X is, if it’s being deposited into the checking account, as you can take it back out. Although I would mix things up a bit, not deposit $100/month and withdraw $100/month.
As to resetting the rate, how long before the end of the 90 day period ? If it’s recent, you can send an ACH, after it posts call Navy and say you were distracted by a family emergency, you’ve now setup the DD, can the rate be reset?
If someone sez that’s not a DD, but an ACH, just try saying I asked that a monthly DD be setup, and that’s what they said they did. Also, they may be expecting the DD to originate from the military, but you can say you already have that check DD to your bank, so you just asked the bank to setup a DD to NFCU.
Worth a shot.