The Benefit of the Complete Divine wild feat Serpent's Venom says
You can spend a usage of wild shape to gain a secondary bite attack (at your base attack bonus −5 and adding 1/2 your Strength bonus) that deals bludgeoning, piercing and slashing damage equal to a dagger appropriate to your size (1d4 for Medium, or 1d3 for Small). In addition, the bite delivers a toxic venom (Fortitude save DC 10+ 1/2 your HD + your Con modifier; 1d6 Con/1d6 Con). (84)
The Benefit of the Races of Stone wild feat Stone Form says
As a standard action, you can spend one of your uses of wild shape to assume a stony and rocklike form. While in this form, you gain a +4 bonus on Fortitude saves against poison. Your natural armor bonus becomes +4 (replacing any natural armor bonus you normally have, though you retain any enhancement bonus to natural armor).
You also gain a slam attack that deals bludgeoning damage equal to a morningstar appropriate to your size (2d6 points for Large characters, 1d8 points for Medium characters, 1d6 points for Small characters). (144-5)
None of the descriptions of wild feats that I've found (e.g. here) mention a standard duration for wild feats (in fact, many wild feats have unique durations explicit in their Benefits), despite wild shape itself having a duration.
Assuming there's no secret errata for these feats (the Complete Divine errata doesn't mention the first feat, and there is no Races of Stone errata), is the duration of these effects either instantaneous or as per the wild shape use expended to activate the Benefit or determined in some other way that I've overlooked? While a rules-based answer is preferred, if that's unavailable or distasteful, house rules for handling these feats are acceptable.