A timestamp field can be set to auto-enter the current date/time each time that a given record is modified. Will that do what you need?
I think so, can you tell me, if I create a variable in a table called Diary and call it "DiaryTimeStamp" and use the CreationTimeStamp option, does that mean that whenever a new record is placed in the Diary table, the variable "DiaryTimeStamp" will record the time?
You do not create variables in tables. You create fields. Variables are a different object in a Filemaker Database.
does that mean that whenever a new record is created in the Diary table, the field "DiaryTimeStamp" will record the time?
It will auto-enter the date and the time each time a new record is created.
But your original question suggested that you want it to auto-enter the Modification TimeStamp which will enter the date and time the record was modified, not just the point in time when it was created.