Most land snails shun heat and direct sunlight, and need moisture.  I think
those are the principal ideas to keep in mind when looking for them.  In
dense woods that are always moist and cool, you may find snails out and
about during the daytime; but in fields or other open areas, you won't see a
snail exposed anywhere during most of the daylight hours.  Actually this is
an advantage in searching for them.  When they are active, they can disperse
over a relatively wide area, and can be harder to find.  But when conditions
are not right for them to be actively feeding and moving about, they often
congregate in whatever small areas will afford protection from light and
heat.  Good spots for daytime collecting include - under logs, bark, or
other debris on the ground.  This includes manmade debris.  An old sheet of
plywood or pile of shingles will often shelter a good number of snails.  I
have found snails more than once inside the openings of cinder blocks.
Underneath any large rock that has clearance with the ground is good.  If
the rock is embedded in the earth, don't break your back.  All you'll find
is worms.  If a large rock has a sheltered overhang on one side, snails may
be attached to the underside of the overhang.  Along the base of a large
boulder, where it makes contact with the ground, is often good, especially
on the side of the rock away from the sun.  Likewise at the base of stone
walls, either on the soil against the wall or in holes or depressions in the
wall near ground level.  Inside a hollow log lying on the ground is also a
likely shelter.  Check the undersides of large leaves of low-growing plants.
Raking through leaf litter on moist earth is a productive method.  On dry
earth you won't usually find anything alive.  Of course you may find dead
snails that took shelter there before the area dried out.  I would advise
using some sort of tool for this, not your bare hands.  Leaf litter can also
shelter spiders, snakes, and other undesirables.  A friend of mine, on a
business trip to Florida, went out looking for snails in leaf litter and
ended up in the emergency room, compliments of a small rattlesnake.  Daytime
is the best time to look for snails in hiding.  The best time to find them
out and active is early morning, especially after a night rainfall.  Evening
can be good if there is moisture, but if a hot sun has dried everything out
during the day, they may not become active until the morning dew.
        Paul M.