From the 3.5 FAQ (if desired):
"Activating any magic item is a standard action, unless the
item duplicates a spell effect that has a longer casting time or
unless the item description specifies a different casting time.
The sections on spell completion and spell trigger items should
include the caveat that activating the item takes as long as
casting the stored spell would take. Thus, it takes 1 hour to
activate a scroll with an identify spell on it. A scroll or a wand
with any of the summon monster spells in it takes a full round
to activate, just as casting a summon monster spell does"
From the Rules of the Game (if desired):
"If the spell contained in a spell completion item has a casting time other than 1 standard action, that is its activation time. For example, a scroll containing a summon monster I spell has an activation time of 1 round because that's the casting time for the spell."
"Activating any magic item is a standard action, unless the
item duplicates a spell effect that has a longer casting time or
unless the item description specifies a different casting time.
The sections on spell completion and spell trigger items should
include the caveat that activating the item takes as long as
casting the stored spell would take. Thus, it takes 1 hour to
activate a scroll with an identify spell on it. A scroll or a wand
with any of the summon monster spells in it takes a full round
to activate, just as casting a summon monster spell does"
From the Rules of the Game (if desired):
"If the spell contained in a spell completion item has a casting time other than 1 standard action, that is its activation time. For example, a scroll containing a summon monster I spell has an activation time of 1 round because that's the casting time for the spell."