How many active duty days must a reservist complete to register an allotment?

To register an allotment, a reservist must complete a minimum of 180 active duty days. This requirement ensures that reservists have enough commitment and service time before they can set up allotments, which may involve financial responsibilities such as savings or paying for services. Having a longer period of active duty establishes a good standing and reflects the reservist's dedication to their service, making them more likely to be effective in managing their finances responsibly while serving. Shorter timeframes like 90, 120, or 240 days do not align with the established regulations concerning allotment registration, which is why the threshold of 180 days is the correct answer.