http://www.wnba.com/news/inactive_rules.html

Inactive Rules

Rosters show active and inactive players
a. A team may carry a maximum of 2 players on its Inactive List

b. As with the Injured List, the Inactive List will
only exist during the Regular Season.

c. Subject to the rules set forth below, players may
move freely between the Active List and the Inactive List.
There is no minimum period of time that a player must spend
on the Inactive List, once moved there. (Accordingly, the
three-game waiting period that previously applied to the
Injured List has been eliminated with respect to the
Inactive List.) There are no limitations on the number of
times a player can be moved back-and-forth between the
Active List and the Inactive List.

d. Players signed to new contracts during the Regular
Season, or obtained in trades with other teams during
the Regular Season, can be signed or traded directly
to the Inactive List. Unlike the prior rules, such
players do not have to be signed or traded to the
Active List and then transferred to the Inactive List.

e. As with other roster changes, a team must notify
the WNBA Basketball Operations Department. This
written notification should be provided PRIOR to
any game in which the team's Active List will
change from the team's previous game.

f. No roster moves are allowed within the 60-minute
period prior to the publicly-announced start time
of a game. (For example, teams that are scheduled
to play a game starting at 7:30 p.m. may not move
a player from Active to Inactive (or vice versa)
at 6:30 p.m. or thereafter.)

g. At 60 minutes prior to the publicly-announced
start time of a game, the Official Scorer will
first obtain the Active List from the home team.
With this list in hand, the Official Scorer will
then obtain the Active List from the visiting team.
Upon obtaining both Active Lists, the Official Scorer
will then provide the visiting team with the home
team's Active List and the home team with the
visiting team's Active List.