I put out the hummingbird feeder about ten days ago.  They started
using it a few days later.

However, it's just outside the north kitchen window - the one with the
cat shelf on the inside - and the birds and cats were never there at
the same time.  Until this morning.  An iridescent male Ruby Throat
came up to the east window - for a moment I though he might actually
knock on the window - then flew around the corner to the feeder and
proceeded to suck down rather a lot of artificial nectar ... about a
foot from Fleagor's mouth.  Fleagor just lay there watching the bird,
otherwise showing hardly any interest.  Maybe the tiny bird was just
*too* tiny.  It certainly was brave.