Leading Edge devices full extension with ALT FLAP EXT will take 1 minute. Start your Chrono, first 30 seconds you will see the LE flaps extended, end of 1 minute you will see the LE slats also full extended (see this on the LE DEVICES ANNUNCIATOR PANEL - AFT OVHD)
If this does not happen by the end of 1 minute. You can go ahead with ALL FLAPS UP LANDING NNC