We have a study with TRs of 3 seconds, but the stimuli are not TR locked, instead the stimuli are of variable duration (both their onset and offset).

Can we create a stim_times file without first having to create a stim_file (as this appears to be most useful when using a TR locked design)?

If yes:
In the past (before we were aware of the stim_times function) we would create a file for each regressor, consisting of a single column, and each row having both the stimulus onset time and offset time separated with a colon.
Example:
100:120
160:175
180:195

Assuming we can just create stim_times file, could we create individual stim_times files for each stimulus, that would have both the onset and offset time separated with a colon? We have been unable to find an example of how to create a stim_times file that would apply to this sort of design. So if we were using a “global times” format, would a single file that corresponded to a particular condition look something like this?

100.1:120.2
160.1:175.3
180.3:195.4

Where each row is a stimulus? And each case is relative to the start of the first imaging run?

Similarly, if we went with a local time presentation where 2 runs are concatenated together, would it look like this:

100.2:120.3 160.5.1.0:175.2 180.2:195.5
21.2:28.5 50.4:60.3 121.2: 130.5

Lastly, if we can create a stim_times file, is it simply a text file?