Change DNS required to even start seeing the WP replicate of my incoming domain transfer?

I want to transfer my main wordpress site ie something.com on a different dns to inmotion...installed wordpress skeleton and exported the old site with the migration plugin in a 2GB~ file. I want to import the site within wordpress plugins on inmotion to the default domain of something . com.

I put this new primary domain as that primary domain 'something. com' and I know the DNS has to obviously be changed to here, but I don't want my site to be offline for 2 days hoping that the entire export/import works while the new DNS propagates so I can first login here 2 days later...is there a way to actually log-in to the new wp account itself (which obviously is still online with the other DNS)? I didn't change the DNS yet b/c I want a better, faster option to somehow import the site and minimize downtime...if it could be online here simultaneously as replicated, then there is minimal down-time for users.

Or do I have to put 'any' domain as a place-holder website pointed to these DNS to do 'any' work to just get started? Remember, I'm transferring a domain to this server with the same domain name. I don't know why no one answered this anywhere before.