Using an alarm

Should we try to get up spontaneously to meditate or should we set an alarm?

You should use an alarm. To get the special Grace to wake up spontaneously, you have to be a Yogi. But please, when you meditate, do not keep a clock in front of you. If you really want to meditate soulfully, just dive deep within. When you meditate, you are pleasing the Supreme. He will make you conscious of the fact that it is time to go to school or to the office. If you are really meditating, He will do this. But if you are in the sleep world, dreaming and wasting your precious time, it will not be His responsibility.