When can I safely skip to the "end of day"
You do miss these events when you skip the day.
i can not provide a Source for my observations but with around 15hrs into the game I feel confident to give you this advice:
The trader usually shows up quite early. The latest guy i had was around 2.pm but this seems to be only the first one on Day 2/3. Normally he is there within 2-3hrs into the day.
Same goes for other events. Very early into the day.
Trader and other events have never happend on the same Day for me.
So i'll always asume that after 2.pm i can safely skip the day.