Why can't I get inside the grandfather clock in this time?

Purple Tentacle's orders are preventing you.

Or rather, the guard who has to carry out those orders is.

His main job, though, is to take care of escaped humans.

There are some humans in the kennel.

But before you can do anything with them, you'll have to take care of the
"Mr. Tentacle Guy" who's in charge of them.  See the next question if you
don't know how to get rid of him.

The next trick is to get the humans to leave the cell.  Only a few things
will convince them to leave.  Talk to Zed and he'll list them.

Of course, make sure to push the switch to deactivate the force field to the
cell.

A skunk is one of them.  Maybe you can find a skunk.

Or at least something that looks remarkably similar.

Like a black cat.  There's one in the front yard.

Do you notice how he squeezes under the fence every time you try to get close
to him?

Maybe you could use that fact to get a white stripe down his back.

Paint doesn't dry all that quickly.

And neither does white correction fluid.