Setting the temporal calibration is done through Data> Edit Structure... :

This opens a new window where we can see the structure of the dataset, and we can also see the absolute time for each time point. To change the time intervals or absolute time we can simply right-click on any single time point and select the option as needed.

By using the option to Set Time Interval... we can set the interval for every time point in the series.

Note that the time interval is assumed to be the same for every time point. Also, if the specific time is important (e.g. FRAP experiments), it can be set for any of the time points by right-clicking on that time point and setting the date and time.