Does reserve time count towards 20/20/20? The answer is "it depends", and even then, the more military practitioners you ask, the more answers you'll end up with.
10 U.S. Code §1072 does not clarify whether "creditable service" means reserve or active time, but simply requires that the years be "creditable in determining that member's or former member's eligibility for retired or retainer pay". Undeniably, reserve time counts towards reserve benefits - a former spouse married to a reservist for more than 20 years of reserve time is eligible for 20/20/20 benefits upon the reservist actually becoming eligible.
Likewise, undeniably active duty time will count towards reserve benefits, if the servicemember ultimately receives a reserve retirement.
The harder question is whether reserve time counts towards active duty benefits - e.g. the parties were married exactly 20 years, but the servicemember was in the reserves for 5 of those years, and active duty for 15. After dissolution, the servicemember served sufficient time to qualify for a regular active duty retirement. There is no unanimous consensus as to whether the spouse's 5 years of marriage overlapping the reserves counts towards active duty benefits, and I've seen analyses by nationally-known military retirement authorities on both sides of this issue - some say that since the reserves don't use time, but points, a "year" in the reserves is far less than a year of active duty (a "good" year in the reserves could be earned in just a few months, not a full year).
But others point out that the statute cited above makes no distinction between reserve or active time. This position is supported by a 2008 decision of the Defense Claims Appeals Board (case no. 08020701) which interpreted "creditable service" in the context of the 10/10 rule for direct payment of military retirement. There, the Board determined that snice the statute does not distinguish between active and reserve time, as long as there are 10 years of marriage overlapping creditable military service of any nature, the spouse could receive direct payment. That rationale would suggest that a spouse with both active and reserve time would also be 20/20/20 qualified.
