In the U.S., 2:00 a.m. was originally chosen as the changeover time because it was practical and minimized disruption. Most people were at home. It is late enough to minimally affect restaurants, and it prevents the day from switching to yesterday. It is early enough that the entire continental U.S. switches by daybreak, and the changeover occurs midway thru a work shift. On a funny side note, churches tend to find the congregations a tad lite on this Sunday!