Launch = Instant
Loading screen = Around 2 mins
Sign in process = Another 2 mins [most of the time, I have to do this twice due to failed connection error].
Wait, so the app launches instantly but is just slow to connect? Your initial post made it sound like the app was taking a long time to launch.
If it's failing to connect or slow to connect, then there are a couple of other things you can try. Try different servers and different protocols (UDP/TCP) and ports. Make sure you are not logged in on more than the max number of supported devices. Check NordVPN isn't being blocked by your antivirus or firewall. Since you said you are on Windows, ensure Windows is up to date and double check the TAP drivers are installed correctly.
There are a couple of help pages here with other potential solutions you could try:
https://support.nordvpn.com/Connectivity/Windows/1107843562/Troubleshooting-connectivity-on-Windows.htm