This should format the tickmarks
datetick('x', 'dd-mm-yyyy HH:MM:SS AM')
It might go after setting the tickmarks
set(gca,'XTick',[ ... ])
Where in the array you should put the datenum
values of your times.
Consider this minimal example:
x = linspace(now-2, now, 30);
y = rand(30, 1);
plot(x, y)
datetick('x', 'dd-mmm HH:MM')