On an Hourglass Inlet, or Inlet to an Hourglass,
the people coming in to the center do a Snake as they come in.
See the discussion of <ATC> to a Diamond.
\sxvlines{b2e,g3w,g2e,b3w}
\shhourglass{b4n,g4e,g3s,b1s}
before Hourglass Inlet
after
On an Hourglass Outlet, the center diamond does a Drop In and Hinge,
fudging to the appropriate place, while the outsides do a Diamond Outlet.