Most seasons are somewhere between 20 and about 26. It depends on the show.
17.
Currently the plan is to have 17 episodes in each of the last two seasons (series as you call them in the UK), five and six.
16 episodes, or 18 hours. The premiere was two hours long, and the finale is going to be two hours long as well.
Land of the Lost (1974-1976) has 43 episodes in total .