The first parameter (actionType) of the method accepts the following values:
“DC” (document close),
“WS” (will save),
“DS” (did save),
“WP” (will print)
“DP” (did print)

Obviously you are interested in “WS”. However, I suspect, it is going to be tricky to implement the needed functionality with it (or I overcomplicate the things).

You still may try to implement the feature with “OpenAction”. Just compare the document creation date and last modification date (if any and if possible), and display the last modification date if it is greater than the creation date.