My excel spreadsheet that I am reading into matlab with xlsread has text for the time in the format of 11:23:23 AM for example. this is a string with no date associated with it so when I try and run datenum or datevec I get an error Failed to lookup month of year. I also tried str2double but that just gives me a series of NaN . What am I looking to do? I need to convert a series of times in an array and then compute the elapsed time among other things.