Immidir near Arak in Algeria?
Temps in November can be considerably warmer than December. The turning point comes sometime late Nov/early December when cold outbreaks tend to stick and the emperature doesn't recover as the frequency of cold outbreaks increase. There are far fewer days with warm air blowing from the tropics in December.
The following long term mean values are a reasonable guide - all values in degrees C
November minimum: between 12 and 8
November maximum: between 29 and 24
December minimum: between 8 and 3
December maximum: between 24 and 20
Visibility is generally better in December - which is the month of best visibility for much of the Sahara. The days are shortest then though.
I'd go in December.