My script and the 1 page = 1 minute rule

I am close to finishing the 1st. draft of the script and there is something alarming: it looks to be about 60 pages long, which is well short of a conventional feature-length script.
I am sure most of you are aware of the general rule that one page of a script generally equals one minute of screen time. A script must formatting in a certain way, with margins to certain sizes, and the Courier font set at a certain point size (I have a Word template that does all this for me, so I don't know all the numbers offhand). Production companies require this so that they can quite reasonably determine how long the film would be and so much it would cost.
I think if I submit this script to a reading service I can expect them to say either that the script is too short for a feature or that due to the style it is impossible to determine the true length. I think the latter is the truth.
I have been busy this evening timing some of the scenes from the workshop, and even without the insert shots scenes are coming to be one page of script equals two to four minutes of screen time.
I wonder if anyone else has had this problem?