Astro binding to move switches at sunset/sunrise

All:

How are the offsets used … in the example on github there is something like:

rule "example trigger rule"
when
    Channel 'astro:sun:home:rise#event' triggered START 
then
    ...
end

Then it says:
Note: Offsets for each event group can be configured in the channel properties

OK … but where … can this be done in the textual configuration files (oh please let it be so) & if so how & what is the syntax?

Is it in the above like (Note the following DOES NOT WORK!)

    Channel 'astro:sun:home:rise#event,offset=-5' triggered START

or something else?

Trying, learning, but running out of brain,
Bruce