How long can you reserve an N-number?

If one wanted to reserve a unique N-number while they were building a plane,
how long can you keep renewing the reservation (understanding you'd have to
pay a fee each time)?

I thought it was for only a year or so, but faa.gov makes it sound like you
can renew at least once, but didn't see an upper limit on the number of
times.

Anyone know for sure?

Thanks;
Carl