UPDATE
I have tracked down why Dolphin, Kwrite, etc. take so long to open the NTFS 2nd hard drive in my system.
This was my iptables setting:
iptables -P INPUT DROP
iptables -A INPUT -m conntrack --ctstate ESTABLISHED,RELATED -j ACCEPT
iptables -P FORWARD DROP
ip6tables -P INPUT DROP
ip6tables -P FORWARD DROP
ip6tables -P OUTPUT DROP
With this firewall setting, the NTFS drive took over 4 minutes to open in a KDE window.
I added the loopback rule of
iptables -A INPUT -i lo -j ACCEPT
and now it opens instantly.
I have no idea why a firewall setting is affecting KDE's ability to open an internal SATA NTFS hard drive, but it is.
If I remove the loopback rule or set the OUTPUT rule to DROP, the NTFS slowdown reappears instantly.