I just tried adding the timer as a dependency and it works for me
Do you use any other extension? Could it be some trouble with that one?
I do not know. The original timer is saved, but the phone does not work. Project Exploere says that ext.manifest and timer.cpp can not be built.
So I used the timer module provided by britzl. I use it as a module and it works fine.
I've updated the extension to support that timers can cancel other timers in their callback functions. This did previously cause crashes in the extension (a typical case of iterating an array and removing elements at random).