If you want to plot all of the data, but to not connect the line between some values, you could inject a NaN in your data where you want the line to break.
Here's an example of how to do it with brute force:
% Create your data
t = [datetime(2015,1,21,[9:12],0,0) datetime(2015,1,22,[9:12],0,0)]
d = 1:8;
% Inject the NaN into d. and put something into t. Doesn't matter what,
% since it won't plot.
d = [d(1:4) NaN d(5:end)];
t = [t(1:4) t(end) t(5:end)];
% Plot it
plot(t,d)
