I'm trying to setup a daily subscription for people who submit a specific form in only the last 24 hours (ie. not a cumulative report).
Given the daily subscription cadence is in the morning (around 4am I believe), to ensure I am never leaving anyone out, is it best to use "in past 24 hours" or "in past 1 day"?
Let me make a bold statement here: "in past 24 hours" and "in past 1 day" is exactly the same.
Yep, that's the way I see it too. For any time reference Marketo will look back / forward from the moment you run the query, so 1 day and 24 hours would give you the exact same result.
Days usually have 24 hours, but not on Daylight Saving changes! There's one 23-hour day and one 25-hour day in any timezone observing DST.
So it really depends on what exactly you want to happen in these exceptional cases. Unfortunately I think Marketo blends the 2 cases together, turning 1 day back into 24 hours.