I will assume an Excel file "Sample Data.xlsx", which has a column named DateTime with time logs for each data sample, in the format (dd/mm/yyyy hh:mm:ss). MATLAB has the datetime datatype that is automatically associated with the table that is read in. Then the duration in seconds between sample points can be calculated as below.
dataTable = readtable("Sample Data.xlsx");
reqDur = dataTable.DateTime(2) - dataTable.DateTime(1); % Replace DateTime with the column name in the Excel file with the time log
reqSec = seconds(reqDur);
Then, "reqSec" can be used in the "Sample Time" property of the "powergui" of Simulink that controls the sample time for discrete simulations in Simulink.
The documentation on datetime (https://www.mathworks.com/help/matlab/ref/datetime.html#d124e321916) can help in understanding the above code.
