Creating templates for data entry boxes

I’m trying to work out how to create a template / scrip that prepopulates
the Text Area “UpdateContent” on the Update.html page, with an action of

If you have a signature this is inserted into the comment - I’m after
another way of putting text into every comment, that the end user can then
modify. The idea is that this will give them the framework for their
ticket notes - something like:

Start Time:

Problem Description:

Work Performed:


Next Steps:

End Time:

All of the scrip & template wiki entries I can see refer to email-centric
actions - for example “notify Owner on Comment”. What I want is
"Prepopulate Message with Template text".

Is there an inbuilt scrip I can use for this purpose, or do I need to
build a custom action? I’m not clear what object I’d be referring to
either, because strictly speaking it’s not a Transaction Object because it
doesn’t exist yet (i.e. until you hit save). Maybe it’s a content object?
I really don’t know…

For bonus points I’d love to record starting & ending times automatically,
and use this to populate time worked, but one thing at a time!

Where do I start looking?