Out of curiosity: Where did you get that '1 hour' stuff from?
IIRC, PRD claims it takes 1 day (aka 24 hours) to make the bonus count as permanent, thus enabling feats, spells and the like...
If such a thing (a +3 headband of wisdom, by RAW they come in +2, +4 or +6 varieties) exists, and you wear it longer than 24 hours such that it becomes a "permanent" bonus, then you would meet the casting stat requirement for a 9th level spell. A 17th level cleric gets 1 ninth level slot and 1 ninth level domain spell per the cleric table.
Permanent Bonuses: Ability bonuses with a duration greater than 1 day actually increase the relevant ability score after 24 hours. Modify all skills and statistics related to that ability. This might cause you to gain skill points, hit points, and other bonuses. These bonuses should be noted separately in case they are removed.
Slim forgot to mention that the bonus is permanent ONLY so long as you wear the headband. If it gets taken off, lost, stolen, or destroyed, you immediately revert back to original Score.
Needless to say, that means you would lose the ability to cast those spells. Any character so reliant on such an item needs a backup. Prepare Owl's Wisdom daily!
Since Owl's Wisdom does not grant a permanent ability bonus, it would not allow you to cast extra spells, either higher level ones, or additional lower level ones. The text for the spell even points this out:
"Clerics, druids, and rangers (and other Wisdom-based spellcasters) who receive owl's wisdom do not gain any additional bonus spells for the increased Wisdom, but the save DCs for their spells increase."
Even if it did allow you to cast higher level spells, you would likely not have time to prepare them; Owl's Wisdom lasts for minute/level, whereas spells typically take at least 15 minutes to prepare individually (or 1 hour to prepare all of your daily spells.)