day of year hour minute to date?

Constant kSecondsPerDay = 86400
Constant secondsPerHour = 3600

Function EncodedDateToElapsedTime(encodedDateStr)
    String encodedDateStr   // e.g., "2130630"
   
    Variable dayOfYear = str2num(encodedDateStr[0,2])
    Variable hour = str2num(encodedDateStr[3,4])
    Variable minute = str2num(encodedDateStr[5,6])
   
    Variable result = kSecondsPerDay* dayOfYear + secondsPerHour*hour + 60*minute
    return result
End

// ConvertToIgorDateTime(tw, year, outputName)
// tw is a text wave containing date/times encoded like this:
//  2130630 Day 213 of the specified year, time = 06:30
// Example:
//  Make/T testIn = {"2130630", "2130730", "2130830"}
//  ConvertToIgorDateTime(testIn, 2006, "testOut")
//  Edit testIn, testOut
Function ConvertToIgorDateTime(tw, year, outputName)
    Wave/T tw
    Variable year       // e.g., 2006
    String outputName   // Name for output wave
   
    Variable numPoints = numpnts(tw)
    Make/O/N=(numPoints)/D $outputName
    Wave w = $outputName
    SetScale d, 0, 0, "dat", w      // Mark as date/time wave
   
    Variable startOfYear = Date2Secs(year, 1, 1)
   
    w = startOfYear + EncodedDateToElapsedTime(tw)
End