As a rule, I would not sweat the details to this level. The timing of the check is not related to the event. The check merely represents the outcome of the event.For tasks that take time, when is the skill check made? Is it made over that whole duration? Or at the end? Or...?
Again, my instincts say, "This is too much level of detail and is not something you should be concerning yourself with." I legitimately do not believe the designers put this much thought into either of these abilities, primarily because the only timing concern in D&D is with reaction abilities and initiative. You certainly can run your game such that 1 minutes is the cap for guidance, and 10 minutes is the cap for Bardic Inspiration, but I don't think that's necessary nor do I think it's what's intended. I suppose there is ludo-narrative dissonance if you want everything to be hyper-literal or extremely specific, but I don't see why the game should or would necessarily be that way. It's a very gamist style of DMing rather than narrative, and I'm much more narratively focused.One reason I ask is that in another thread, a few posters suggested that a spell like guidance should not work on a task that takes longer than one minute. Implying that the check is made over the duration of the task, rather than at the end. (Because, were it at the end, then couldn't the guidance caster wait until just before the end?)
I think this interpretation leads to imagining that guidance is in operation over the whole 1 minute; but how about bardic inspiration? With inspiration, one has 10 minutes to use the die. I think this interpretation means something like - the task would need to start and resolve completely inside that 10 minutes. Looking then at Lucky, I think this interpretation means that the feat is used at the last possible moment - the instant of task completion. Because, to be consistent, I think we want all the buffs and re-rolls to be occurring inside the task duration.
A residual question is, is it that only one cast of guidance and one inspiration die can be used for a given task? What I mean is, could a magical initiate cast guidance at the start of a 2 minute task, and then recast it 30 seconds in, and then again after another 30 seconds, and then again. Thus with four casts spanning the whole 2 minutes.
I would rule that as long as the task begins, continues or ends within the time limit of the spell or inspiration, then the player may chose to use the spell effect or ability effect with that check.
As DM, I would examine what the likely design intent of the time limit rule is. IMO, the primary design intent is to prevent casting the spell or granting inspiration and then having it around for hours of the game day, effectively making it a permanent effect until used.
Narratively, the cantrip is directly asking your deity for aid with a particular task that another is doing, and whether the deity is affecting the target of the spell from beginning to end or changing the world in your favor at the end, it does not particularly matter. As such, to me the design intent of the cantrip is that it should be useful when the cleric is immediately available to request their deity for aid. In other words, the cleric must be present for the encounter and must also spend an action. It's really a spell equivalent of the Help action, with a very small bit of extra time for practicality purposes. Still, the spell's duration implicitly says, "Something that happens during this encounter while the cleric and his subject are present." The limitation also makes it fairly impractical for use during combat (or, at least, no more practical than the Help action itself is). It's also of fairly limited use during social encounters because it's a little aggressive to start casting spells -- even blessings -- when one of your party members is just asking questions (remember, it's verbal, somatic, and range touch). To say it looks sketchy to cast in the middle of a Diplomatic check would be putting it mildly. Not that you couldn't use social skills with the cantrip, just that it's much harder to set up.
The design intent of Bardic Inspiration allows more leeway, simply because an inspiration die is a much higher cost than a cantrip action. Otherwise, it's largely the same idea. You might be able to activate it in one encounter and not use it until the next encounter if your party doesn't stop to search. You're also much more reasonably able to use it before a social encounter and still have it be useful for quite some time.
Bottom line, though, it doesn't really matter either way as long as you're consistent. Though, if you rule that guidance only works on tasks that take less than a minute and then arbitrarily rule that most tasks take more than 1 minute, you're just soft banning the spell. It would be better to alter the spell or outright ban it.