From Longman Dictionary of Contemporary Englishlast thing (at night)last thing (at night)LATEat the very end of the day Take a couple of these pills last thing at night to help you sleep. → last
Examples from the Corpuslast thing (at night)• I agree with that last thing.• Take a couple of these pills last thing at night to help you get to sleep.• The last thing he said to me last night: I still want that money.• It was the last thing he wanted to do.• Working is the last thing on their minds.• The last thing Republicans need is a nominee who runs from the Republican House, who is defensive about their agenda.• The last thing she felt, apart from the pain, was surprise.• The last thing that I want to do is stray out of order.• The last thing you need is confusion over that.last thing at nightlast thing at nightLATEat the end of the day, just before you go to bed You should water plants either first thing in the morning or last thing at night. → night
Examples from the Corpuslast thing at night• Why not set a few moments aside first thing in the morning and last thing at night?• The only times my father could be found in his room were first thing in the morning and last thing at night.• Empty ashtrays last thing at night, and don't smoke in bed.• Lock the doors and turn off the lights last thing at night.• This can be carried out last thing at night, once the puppy has been outside to relieve itself.• The rosary last thing at night.• The soldiers are supposed to polish their shoes last thing at night.• Of course, only in moderate quantities, and generally to be taken last thing at night.• It was after dark; the last thing at night.• It's the first thing I look at when I wake up, the last thing at night.