Usually the expected time of arrival will get later when you hit peak hour, getting highest when you go the same direction as most of the traffic and as such meeting the most traffic jams.
These will be adding more time in cities with bad traffic flow.
It will not be one given time for all of a country/time zone and even less for all the world.
There will be different times for different cities and different directions of travel. Into a big city in the morning will usually be much longer than traveling out of the same city.
Worse may be if you have a ferry that has big gaps in its schedule. Like to an island which has a break for the night, so if you would arrive just after the last ferry of the day the expected time of arrival will be after the first ferry the next day, if you do not get a 'can not calculate' message.
If there are special circumstances, like road closures due to work that change the averages and road closures due to accidents that change it for 'travel now' calculations.