This problem has been since I installed Mint 18.3 onto an SSD, and continues to this day: now using Mint 19 with KDE, but the problem is at the SDDM login screen.
From POST to login screen appearing is about very quick, but then I have to wait about 30s before the keyboard and mouse initialise.
/var/log/Xorg.0.log shows almost 43s of no activity, eg.
[ 24.472] (II) config/udev: Adding input device HD-Audio Generic Front Headphone (/dev/input/event18)
[ 24.472] (II) No input driver specified, ignoring this device.
[ 24.472] (II) This device may have been added with another device file.
[ 67.350] (II) config/udev: Adding input device PixArt USB Optical Mouse (/dev/input/mouse0)
[ 67.350] (II) No input driver specified, ignoring this device.
[ 67.350] (II) This device may have been added with another device file.
[ 67.365] (II) config/udev: Adding input device Microsoft Comfort Curve Keyboard 3000 (/dev/input/event3)
[ 67.365] (**) Microsoft Comfort Curve Keyboard 3000: Applying InputClass "evdev keyboard catchall"
It's not a huge problem, but it's something I'd like to fix if possible. Any ideas?