Added check to ensure we are in lighttable view prior to callling darktable.register_lib. If darktable was invoked in single image (darkroom) mode, then an event handler is registered to detect the change from darkroom mode to lighttable mode so that we can then call darktable.register_lib.

contrib/image_time.lua

@@ -110,6 +110,8 @@ local ds = require "lib/dtutils.string"
 local gettext = dt.gettext
 
 local img_time = {}
+img_time.module_installed = false
+img_time.event_registered = false
 
 du.check_min_api_version("3.0.0", "image_time") 
 
@@ -390,6 +392,22 @@ local function reset_widgets()
   img_time.adir.selected = 1
 end
 
+local function install_module()
+  if not img_time.module_installed then
+    dt.register_lib(
+      "image_time",     -- Module name
+      _("image time"),     -- Visible name
+      true,                -- expandable
+      true,               -- resetable
+      {[dt.gui.views.lighttable] = {"DT_UI_CONTAINER_PANEL_RIGHT_CENTER", 100}},   -- containers
+      img_time.widget,
+      nil,-- view_enter
+      nil -- view_leave
+    )
+    img_time.module_installed = true
+  end
+end
+
 -- widgets
 
 img_time.widgets  = {
@@ -528,13 +546,19 @@ img_time.widget = dt.new_widget("box"){
   img_time.stack,
 }
 
-dt.register_lib(
+if dt.gui.current_view().name == "lighttable" then
-  "image_time",     -- Module name
+  install_module()
-  _("image time"),     -- Visible name
+else
-  true,                -- expandable
+  if not img_time.event_registered then
-  true,               -- resetable
+    dt.register_event(
-  {[dt.gui.views.lighttable] = {"DT_UI_CONTAINER_PANEL_RIGHT_CENTER", 100}},   -- containers
+      "view-changed",
-  img_time.widget,
+      function(event, old_view, new_view)
-  nil,-- view_enter
+        if new_view.name == "lighttable" and old_view.name == "darkroom" then
-  nil -- view_leave
+          install_module()
-)
+         end
+      end
+    )
+    img_time.event_registered = true
+  end
+end
+