Do you actually need to change the time entries, or do you just need to have them display as years?
Changing the time entries could give challenges if it ended up with duplicate row times.
If you just want to change the display then,
c.Properties.RowTimes.Format = 'uuuu';
If you need to change the actual times then
c.Properties.RowTimes = dateshift(c.Properties.RowTimes, 'start', 'year');
Note that shifting to the start of the year is not enough to change the display to be just year.
