Couple of notes: - instead of _to_string(), you can use format(): timer = '%d:%02d:%02d'.format(hours, minutes, seconds); - don't call timeout_add() from the timeout function itself; just return true (or GLib.SOURCE_CONTINUE) to have the function called repeatedly - in disable(), you don't have to remove the button from its parent before destroying it; however you do need to remove the timeout source - rejecting because of that

Thank you for your notes! They are all very useful, but timeout function won't restart itself by returning true. I left it as it was. Please, check version 2.

Uhm yes, that's how GSources work. Note that only the return value of the actual timeout function is used, so when you write timeout = Mainloop.timeout_add(1000, function () { _refresh(); }); that's not _refresh(), but the anonymous function that calls it. timeout = Mainloop.timeout_add(1000, function () { _refresh(); return true; }); should work as expected.