Looks like SetTimeRange() expects the values in VT_Date format, or Variant date/time format.
There is an example in the following file in JavaScript.
C:\Program Files\BigFix Enterprise\BES Server API\TestAPI.htm
// Set the range of Times of the day during which the action is allowed to run.
// This sample will set it to run between the hours of 1 and 3 in the morning. var oneam =
new Date(); oneam.setHours(1); oneam.setMinutes(0); var threeam =
new Date(); threeam.setHours(3); threeam.setMinutes(0); actionCreator.SetTimeRange(oneam.getVarDate(),threeam.getVarDate());