The following picture and story is the restult of a genuine auto-sync over night and not from a manual sync! It all happened during the scheduled switch to DST.
Last night I found that my wife left this watch (which is her running watch), next to the bathroom sync.
While I was preparing to go to bed, I glanced at the watch and saw it attempting to auto-sync. This happened around 0.07, which I found already unusual, given that my watches always gave up after a few minutes after trying to sync unsuccessfully. But this fellow just kept trying, with the signal strength indicator switching between strength levels, while mostly at L3.
At 0.15 the watch was still trying to auto-sync, which I thought was getting just stranger. So I left it as is and went to bed. Curiously following up the next morning, this is what I have found:
Assuming that this watch is programmed to initiate auto-sync at every hour (just like my other watches that are working on US-American 'overnight sync-schedule') and it did not initiate another auto-sync attempt on it's own at 0.30, then this appears to be the most resolute auto-sync attempt ever.
Considering that the switch to DST bumped that result with an extra hour this suggests an auto-sync length of 42 minutes.
This watch just would not give up!