How Do You Move From Hosting to another with No Downtime or DNS Propagation Delay?

How Do You Move From Hosting to another with No Downtime or DNS Propagation Delay?

Usually Name server changes usually take 24 to 48 hours to fully start working, which may take lot of time for DNS Propagation and website usually get down at some point,

So, how it's possible to do it without much of downtime ? any ideas ?