Acars clock maybe?
Other 'trick' if you are after block hours (tut tut - as if
) is to release and reapply the p/brake just before main door opens if you have been waiting for a while for those pesky ground staff (good trick for BA during the 30 min wait for jetty). 'IN' is, as FO says, (I think) transmitted when main door opens using last brakes on time. Regarding 'OUT' - I'm not sure it reads main door time - I think it uses last p/brake off and again is sent on main door signal?