The time component of a UTC date time object may be separated with : (for the extended format), or with nothing (the basic format).
When called with the default argument of 'true' the terseCurrentTime function produces the extended format. However, the extended format's use of : as a separator makes it invalid as a filename.
When called with 'false', terseCurrentTime uses the '-' character to separate the time components, which results in a format which is not compatible with ISO 8601.
We should either fix the function to remove any separator in the time component when the function is called with 'false', or update the documentation of the function to make clear that it does not produce UTC date times in that case.
Note that our log file extension currently reflects the results of calling terseCurrentTime with 'false'.