Both of these functions in the Trading Toolbox call IB's reqHistoricalDataEx function internally, but for some reason Mathworks chose to make a distinction between historic data for full days (period=day/week/month) and intraday data (barSize<1 day). Note that these 2 functions are not consistent in the order of the input arguments and their name (period/barSize), although they use the same basic internal mechanism.
As an alternative that offers consistency and additional flexibility in the historic data parameters, you could try my independent IB-Matlab connector.
