I have worked out my version here if anyone needs it in future.
dateNumArray = []; %// Store datenums here
%// Enter a blank line to quit this loop
while true
timestr = input('Enter a time: ', 's');
if (isempty(timestr))
break;
end
%// Split the string up at the ':'
splitStr = strsplit(timestr, ':');
%// Read in the current date as a vector
%// Format of: [Year, Month, Day, Hour, Minute, Second]
timeRead = clock;
%// Replace hours and minutes with user prompt
%// Zero the seconds
timeRead(4:6) = [str2num(splitStr{1}) str2num(splitStr{2}) 0];
%// Convert to datenum format
dateNumArray = [dateNumArray datenum(timeRead)];
end
