Propagation is the wrong word
Nothing spreads outward from your registrar. When you change a record, every resolver that already asked keeps using the answer it has until the TTL on that answer expires. Until then it has no idea anything changed, and no way to find out.
So when two resolvers disagree, nothing is broken and nothing is in transit. One of them is simply holding an older answer that has not expired yet.
Which means the TTL is the real answer
If your TTL is 3600, a change can take up to an hour to be seen everywhere. If it is 86400, it can take a day. The number is entirely predictable and entirely under your control.
Before a migration, lower the TTL and wait for the old one to expire. Drop it to 300 a day ahead, make the change, then put it back. Lowering it during the migration does nothing, because the old TTL is already cached.
More in the TTL field guide and moving DNS without downtime.
See also