The rod of wonder (DMG 237) creates Wondrous Effects that have printed durations, creates Wondrous Effects that mimic spell effects yet don't include printed durations, and creates Wondrous Effects that don't mimic spell effects and that don't have printed durations.
Are the durations of these last kind of Wondrous Effects instantaneous (PH 176)? That is, are these last kind of Wondrous Effects unaffected dispel attempts?
I know the rod's a joke item. I know it's a relic of an earlier gaming era. I know about the greater rod of wonder. Heck, I even know I "may alter any of these [Wondrous Effects] as [I] see fit for [my] own campaign" (DMG 237).
But I'd still like an answer.
Below is all just food for thought.
Effects with Printed Durations
These are, obviously, are easy to adjudicate. For example, 01-05 says, "Slow creature pointed at for 10 rounds (Will DC 15 negates)," and 11-15 says, "Deludes wielder for 1 round into believing the rod functions as indicated by a second die roll (no save)."
Effects Mimicking Spells yet Lacking Printed Durations
These are a little harder, requiring look-ups or some minor DM ruling. 06-10 says, "Faerie fire surrounds the target," thus requiring looking up faerie fire [evoc] (PH 229), finding the spell's duration of 1 minute per caster level, and determining that the rod's caster level of 10 makes the faerie fire effect's duration 10 minutes. 34-36 says, "Summon an animal...," without noting a specific spell reference--some DMs'll rule that the rod's summon is as per the summon animal spell, while other DMs'll rule it's as the creature ability summon (MM 315), but, long-term, that's a distinction without a difference.
(A serious but unattractive argument can be made that these effects should be instantaneous in addition to the last category's effects being instantaneous. Yes, serious because while some items have durations, others don't, so obviously these are instantaneous effects. Yes, unattractive because while the durations aren't printed there they absoutely are referencing the spells, and the spells they're based on do have durations that can be checked. And since they can be checked, only willfull literalness prevents the DM from doing so.)
Even though it lacks a corresponding spell effect, when 96-97 says, "Wielder (50% chance) or target (50% chance) turns permanently blue, green, or purple (no save)," it's duration is permanent, so the effect's subject to dispel attempts versus the default rod's caster level of 10. If the effect must have a spell level (e.g. someone checks out the purple dude with detect magic, an area dispel magic is used instead of a targeted one) the DM could set the spell level at 3rd or 4th (the level of the spell confusion [ench] (PH 212) the wizard or bard used to make the rod) or maybe 5th (half the typical creator's HD as per determining the saving throw DC of a supernatural ability), but that's trivial in the grand scheme--really, that's just a matter of some purple dude hording gp until he can afford to be depurpled. Unpurpled. Whatever.
Effects Not Mimicking Spells and Lacking Printed Durations
These are brain-breakers.
63-65 says, "Turn ethereal any nonliving object of up to 1,000 lb. mass and up to 30 cu. ft. in size"--so while that's not a terrific size, it's certainly enough weight to arm (depending on the DM) with +1 glaives your ghost legion that was created by judicious use of the 4th-level cleric spell raise ghost [conj] (Gh 57). Further, it's more than enough weight and size to turn forever ethereal most published artifacts--not destroyed, obviously, but ethereal instantaneously, so the artifact can't just be grabbed and hauled back to the Prime, and that's where most of the interesting stuff happens. Note that 63-65 really says, "Turn ethereal," not, "Turn ethereal," so even the reference to the spell etherealness [trans] (PH 228) isn't there except insofar they share the first 9 letters.
66-69 says, "Reduce wielder to 1/12 height (no save)." This either makes a Medium wielder Diminuitive and a Small wielder Fine or gets really wacky. If the former, while the 1st-level wizard spell reduce person [trans] (PH 269) (which this effect isn't) allows a "minimum of 1" Strength after being targeted by it and the 8th-level wu jen spell minute form [trans] (CAr 115) (which this effect also isn't) says that "[n]one of your ability scores can be reduced below 1 by" minute form, the template dungeonbred (Du 113-4) specifically refers to Monster Manual 291 for reducing a creature's size category. Reversing the statistical alterations from Table 4-2: Changes to Statistics by Size results in a -10 penalty to Strength when dropping the 3 size categories that 1/12 height usually means, turning 1 in 25 first-time rod of wonder wielders from stalwart adventurers into highly detailed (in)action figures. If the latter, and it's only height that's reduced, the DM can totally say, "You're height is reduced to 1/12, but it doesn't say your size category changes, so you look kind of like a fat pancake and this has no game effect," which is weird, but so's that DM.
91-95 says, "Shimmering colors dance and play over a 40-ft-by-30-ft. area in front of the rod. Creatures therein are blinded for 1d6 rounds (Fortitude DC 15 negates)." Does this create an area in which these colors dance and play forever? Read it again then ask: Does this area move with the rod?
(As an aside the spell break enchantment [abjur] (PH 207) should fix the creature-affecting stuff if the DM determines the effect's spell level is 5th or below, and the spell ruby ray of reversal [abjur] (SpC 177) should fix the creature-affecting stuff no matter how high the DM sets the effect's spell level. That's probably a relief to G. I. Mialee and Nebin the Pancake Gnome but not much consolation to Regdar when some ghost scoops up his now-ethereal sword of Kas.)