Unable to use times for fill-in-the-blank answers

When I make a fill-in-the-blank object, I am unable to specify a hh:mm time as one of the answers. For example, trying to use 11:00 as the correct answer results in H5P suggesting that two answers are correct: "11" and "00". This is perfectly in keeping with the markup understood by H5P where a colon indicates an alternate answer.  I tried escaping the colon in the markup (11\:00) hoping that it would then be treated as raw text and allow , but that did not work.

How can I allow the use of a hh:mm time format in a fill-in-the-blank answer?  The project is for a training that can't change to another format.