"Value must be a vector of increasing datetime values."
set(gca, 'Xtick', (0:100:1200), ...
Those values above are not datetime values. They are double precision numeric values.
Assuming 'interval' contains datetime values, try,
set(gca, 'Xtick', interval(1,1):minutes(3):interval(101,1), 'xlim', interval([1,101],1))