Originally Posted by K-Man

"Generally, members of the U.S. armed forces who serve honorably for any period of time (even 1 day) during specifically designated periods of hostilities (see below) are eligible for naturalization under section 329 of the INA through such military service."

Technically you can get it signed after 1 day of drill (actually 2 fiscal days/or a weekend, which add up to 1 day of service). If you have more drills they'd be more inclined to sign it since they know you, but you definitely don't/won't have all 48.

I think I went to half dozen drills at most since my enlistment.