Java normal distribution

nextGaussian() will draw samples from a normal distribution with mean 0 and std-deviation 1, so if you want mean 1 hour and std-deviation 15 minutes you'll need to call it as nextGaussian()*15+60.

From the docs for Random.nextGaussian():

Returns:
the next pseudorandom, Gaussian ("normally") distributed double value with mean 0.0 and standard deviation 1.0 from this random number generator's sequence

I suggest you to use apache math: http://commons.apache.org/math/ , look here for more information: http://commons.apache.org/math/userguide/stat.html