Irwin pretty much shared monsters only between Lost in Space and Voyage. The Lost World dinosaur footage wound up on all of his shows, but the actual monsters stayed off The Time Tunnel. However, the alien makeups did get reused. Silver face paint was his standard, but the some of the alien heads and his "white nylon over the face" masks usually reserved for androids hit Time Tunnel. by the end.
Irwin's shows had a habit of front loading the money. The first episodes of each of his series were usually more impressive than later. The Time Tunnel, though, still always had normal to large guest casts. Voyage was the very definition of "bottle show" by its third season, with maybe one or two guests mixed among the background players. Often, stories would be written to give the Seaview a skeleton crew while a dude in a sheet or a disembodied voice would threaten the crew. Or, as Irwin was most fond, one of the leads either brainwashed, taken over, turned evil or a dastardly duplicate.
Lost In Space could get away with just the main cast and one alien per week on standing sets, but by the end of the second season, it was looking like a children's stage play. It felt as if money which should have been spent on those shows was poured into The Time Tunnel, at least as far as paying actors and somewhat better writers (Voyage had William Welch penning most of them and LIS had Peter Packer). However, over the run of the series, even the guest actors were low salary character actors or Irwin's regular standbys.
Time Tunnel could be a great show for the day when it tried, there was some very strong episodes in the beginning. Then it settled for just being fun, but at worst, it was dull. Not as much of a chore as Land of the Giants, which was the same thing every week until they embraced the goofy in the late second season.
