How to start a low-freq timer after file-load?

blender 2.8
how to start a low-freq timer after file-load ?
(from addon code)

yes, there is the new timer api. link
I CAN start a timer with a button (operator) call !
but how do I start it after a file is loaded ?

yes, I tried to start it from load_post handler … .load_post .append( handler )
but it does not work, does not start the timer.

(eventually it starts, but the context is invalid ?)

what I actually need is a notification-handler, when active object changes,
if there is any alternative !? ?