In 12 hours: Either about to go to sleep or asleep.
12 hours ago: Falling asleep.

3:37 AM.

In 12 hours - sleeping, or perhaps lying awake dreading the next day
12 hours ago - drifting off to sleep

In 12 hours I will be sitting in a coffee shop with my friend, discussing her trip to Europe and planning our own American road trip.
Twelve hours ago I was watching Six Feet Under.

In 12 hours I will be eating breakfast and awaiting contact from school.
12 hours ago I was still asleep.

in 12 hours ...... i will be at dance class
12 hours ago ..... i was getting home from stage school

In 12 hours: Doing homework.
12 hours ago: Doing homework.

Makes my life sound dull, no?

in 12 hours ..... i will be watching tv
12 hours ago ...... i was alsleep

In 12 hours I will be asleep.
12 hours ago I was lying awake listening to my iPod because I couldn't sleep.