I would like somebody to check my logic, please.
Guidance "imbues the subject with a touch of divine guidance. The creature gets a +1 competence bonus on a single attack roll, saving throw, or skill check. It must choose to use the bonus before making the roll to which it applies." Also note that you can wait up to a minute before activating the guidance.
So could you spend several rounds just casting guidance on yourself multiple times, and then use the guidances over the next few rounds? I know you shouldn't be able to use multiple guidances on one action, but is there any restriction to having multiple guidances hanging around for use on different actions?
actually I think mdt is wrong. While they don't stack for a single action nothing I know of prevents you from having more than one on you as a time (stoneskin either.)
That said, with guidance you aren't going to get much out of it, the absolute max you could have on you is 10, since be they time you go to cast the 11th the first is worn off. In reality, times that you know you will be in a fight in X number of rounds is far more limited than that, particularly since if, for example, you start casting spells outside the door you are going to bust open, it is likely that whatever is on the other side of that door will.
This is the closest thing that address this directly in the CRB:
Same Effect with Differing Results
The same spell can sometimes produce varying effects if applied to the same recipient more than once. Usually the last spell in the series trumps the others. None of the previous spells are actually removed or dispelled, but their effects become irrelevant while the final spell in the series lasts.
Based on that, you would have to use the guidance in a last-in first-out order, which limits how many you have even further.
If I cast six guidance in a row, I have only 4 rounds to use all of them before the first one's duration has expired, and I have to use that first one after I have used each of the others.
I think you are wrong, but it's arguable either way. The problem with that section is that it applies to spells with differing effects. Casting guidance multiple times doesn't apply different effects. It would if you could specify the type of check (+1 to Attack roll on 1st casting, +1 to Save on second, etc). But all the guidance spells would have the same effect, which means that section doesn't apply.