[christianmann]

Maybe so, but you can pretty reasonably assume that most people are awake and active at 1:00 PM in their time zone.

[moooo99]

You can. But especially if you don't have frequent contact with other timezones it is very hard to keep track about how far they are ahead or behind your local time. This gets even harder with DST. While this might be easy if you're just in different US timezones, but it gets increasingly harder with larger distances.