Note that the format of the datetime array is irrelevant. It is only used for display. You could of course change the Format so that it only shows hours and minutes but calculations would still involve the date as well.
You use the hour and minute functions to extract the hours and minutes from a datetime array. Alternatively, you use the Hour and Minute properties of the datetime object.
d = datetime + hours(1:10)' + minutes(1:10)'; %create demo datetime a array
hour(d) %get the hour
d.Hour %another way
minute(d) %get the minute
d.Minute %another way
As for the plot, I'm unclear what you want to do. If two values have the same hours and minutes but different day, do you want to plot them at the same abscissa, like a scatter plot?
