Hi Jan, you do not mention the release you are using, but you can put the data in a timetable with the RowTimes equal to whatever they happened to be and those should be preserved in the convenience plot.
x = cos(2*pi*32*t).*(t>=0.1 & t<0.3)+sin(2*pi*64*t).*(t>0.7);
wgnNoise = 0.05*randn(size(t));
tt = timetable(x(:),'RowTimes',seconds(t'));
Now you see that the x-axis in the plot has the correct range. Here t was a duration array, but it can also be a datetime array.
Hope that helps,