Yes, this is a millipede.  You can see the 2 pairs of legs per segment that is characteristic (centipedes have one pair of legs per segment) of them.  They feed on decaying organic material and prefer moist conditions, so are usually active at night.  Sometimes during wet springs you see them - as you have, and as you have also seen they disappear  in the drier afternoon.  They provide a good function in the garden by processing decaying organic matter.  They don't eat plants and won't bite.  As weather conditions dry they will seem to disappear.  Insecticides really don't work on controlling them.  This article gives additional information, Millipedes  https://hortnews.extension.iastate.edu/millipedes.