A four horse day

A four horse day could mean a couple things, depending on who is speaking.

For example, it could mean:
"It's a very busy day at work"
Or
"It's nice to have so much free time to ride my horses"

A popular saying in the 20's, it had disappeared for several decades but has been making a comeback in recent years.

I can come out for one more, but I've got a four horse day tomorrow so I want to hit the hay before too late.

Man, I've been working so hard lately, can't wait for Sunday, it'll be a real four horse day!