I wonder if we'll ever find out why no Time To Kill. It really doesn't make sense. Perhaps the elements are very poor (I've never seen it on TCM or Fox) and they don't want to pay for a restore? Maybe it's something to do with rights as Richard speculated. It is probably the biggest mystery of the entire Mike Shayne series.
I wonder. When Fox released Michael Shayne Mysteries Vol. 1 - ELEVEN YEARS AGO! - it certainly appeared that they had restored all of them and had every intention of releasing a second volume which would have included Time to Kill. There were only seven Fox Shayne films, so it wouldn't have made any sense to release a second volume with just two of the remaining three films.
In any event, Fox has treated the fans of the films very poorly. The release of something titled Volume 1 is an implicit promise that there will be a Volume 2.