solved:
T = 1000;
time = 1: T;
x1 = rand(T,1);
x2= rand(T,1);
myTime = {...
'08:00'
'08:10'
'08:20'
'08:30'
'08:40'
'08:50'
'09:00'
'09:10'
'09:20'
'09:30'
'09:40'
'09:50'
'10:00'
};
[AX,H1,H2] = plotyy(time,x1, time,x2);
linkprop(AX,{'Xlim','XTickLabel','Xtick'});
t3 = linspace(0, T, size(myTime,1));
set(AX(1), 'XTick', t3);
set(AX(1), 'XTickLabel', myTime);