Daylight savings officially begins every year, on the 2nd Sunday in March.

But, why re-set the clock at two o'clock in the morning?

The general reason is that it is late enough, so that most people would be at home during this time, so it would affect the fewest number of people who are still out, either working or having fun.  

Also, during the fall (when the clock goes back one hour) it prevents the date from switching back to yesterday, which would happen, if the time changes at one o'clock, instead of two o'clock.

The time is also early enough, that the clock time changes before any early morning workers would actually get up for work, so there is no confusion about the time they need to report to work.

Therefore, changing the clock one hour at two o'clock is convenient for most people, who simply change the clock back before they go to bed, and then wake up with with the new time on their clock. 

Just remember to go to bed an hour early on Saturday night, since you will lose an hour's sleep the next morning, especially if you have scheduled something to do the next morning.