Greetings @piper3330 ,
Great question! And I can see you’ve already got some awesome feedback from Amaris and Siofra 

After thinking on it for a bit, I would say that, in terms of casting, there are Two Main Types of Spells:
-
Immediate - these are spells that are prepped, acted on, and ended within a short span of time. While the spell results may linger for a longer period of time (think: amulet charging, protective shield, etc) or the spell may take a while to bear fruit, it has either been put into action or passed on to the Universe, your deities, etc- the spellwork is out of your hands.
For immediate spells, the spell is cast as soon as you finish your spellwork- this may be the last line of the chant, the words “So Mote it Be”, the spell candle going out, or ending your meditation/visualization/etc.
-
Ongoing - these spells are cast over a longer period of time and require ongoing maintenance from the caster, who often needs to continue putting energy and/or ingredients into the spell. A money bowl, ancestor altar, or offering routine are examples of ongoing spellwork.
Ongoing spells are technically being cast all the time or at set intervals- they stop when the caster ceases feeding them. Some may stop working immediately while others may fade out after a while, but without new incoming energy, ongoing spells will dissipate and finish.
(There’s also some spells- like the 7-day money spell- that would fall in between these two types- this certainly isn’t a strict categorization
)
The different types of spells function differently, and on top of that every spell is unique- I suppose you’d need to closely examine the spell you want to re-cast to find when it was cast/ends before re-casting.
Additionally, just a friendly reminder that some spells, even though they are out of your hands, are still being working on by higher powers- just because you haven’t seen a result yet doesn’t mean it isn’t coming!
I cast a very specific spell several weeks ago, waited a few days, and thought it was a bust. But the exact answer I wanted came- just significantly later than I had expected it to. It was a reminder that the Universe isn’t bound by time like we humans are 
Wishing you all the best with your spellwork and casting, Piper- Blessed Be! 