To enter comments during a live observation, we can not pause nor replay the situation. Thus, there is no use for an Event with duration if we want to enter a comment.
In such cases, the following scenario could be useful:
▪To easily create Events without duration, click Start - Observation - Define Codes 
.
▪Clear the SPACEBAR is treated as a Code with duration check-box at the bottom of the dialog.
▪Select the Enter comment after coding with SPACEBAR checkbox.
▪Set the coding mode to Standard, in the Start - Observation - Observation settings 
.
▪Select Live-Observation as your observational source.
▪Click OK to confirm your settings.
▪Click 
, to activate the logging mode.
▪The moment something noticeable happens, press the SPACEBAR once, to enter a Marker.
▪Enter the comment into the appearing dialog.
▪Press RETURN to close the dialog.
▪Continue as described before.
Note: You can also use this functionality to enter comments for situations that are not covered by your Coding scheme, especially if you log your regular Events with any kind of predefined Codes instead of the SPACEBAR.