Latest date the ACW can be pushed to?

What is realistically the latest date in time the american civil war could have been pushed too before starting?

On that note what effects would the advancements in weaponry have made on the battlefield? such as widespread cartridge rifles instead of muzzle loaders.
 
Potentially indefinitely with the right POD and butterflies. There was nothing fated about the ACW; hell as late as 1860 it could have been averted IMHO.
 
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