Last Modified in Gnome Files (Nautilus)

$ gsettings get org.gnome.nautilus.preferences default-sort-order
'name'
$ gsettings set org.gnome.nautilus.preferences default-sort-order mtime
$ gsettings set org.gnome.nautilus.preferences default-sort-in-reverse-order true

From here: https://askubuntu.com/questions/252771/how-to-change-default-sort-by-to-type-in-nautilus

Determine the current default value of Nautilus sort order using gsettings

gsettings get org.gnome.nautilus.preferences default-sort-order

Then change/set it to ’type'

gsettings set org.gnome.nautilus.preferences default-sort-order 'type'

The change happens instantly.

Change type to mtime to sort by Last Modified. You can also set default-sort-in-reverse-order to true to sort in reverse order.