I used [num txt raw]= xlsread(sprintf( 'SMPS%d.xlsx',n),'Data'); to read the excel files. The raw variable is of dimension (480*109). The first three columns are "sample no, date , time". The original format for time is HH:MM:SS but in Matlab the time column has values 0.0035,0.0056,0.0077 etc. I want to convert this whole column to actual time values as i have to further process this using time.