In the case where the x axis is to be a duration array (rather than a datetime array):
First, plot something using an x axis in the same time units as you want the imagesc to be labeled with.
Then
hold on
h = imagesc(I);
set(h, 'XData', [1, seconds(t(end))]);
Modify the "seoonds" to the appropriate time measure. The purpose of the seconds() there is to strip off the duration class, converting the t values to pure numeric values. image() will treat the numeric values as if they were in the active duration units.
This is, of course, a hack.
If your values are datetime arrays then it appears you can do something similar. It appears that the default XData for the imagesc() will be converted into days, probably relative to the first date (but double check -- it might perhaps be relative to the month of the first date.) You cannot use days() on a datetime array to convert to number of days, but you can do
set(h, 'XData', [1 days(t(end)-t(1))]);
You might need to play with the boundary conditions a little.
