I need help with the wording for the sign I put on my door at work when I'm pumping.

I was thinking this:
"Please come back in 10 minutes.
(9, 12, and 3)
Thanks!"

It takes me 10 to 15 minutes to finish pumping. I worry the time part isn't clear - whether it's come back at 9 or I started at 9 (I started at 9). I also wonder if I should even put a time frame on there, as I don't always start at 9 on the dot and would hate for someone to bust in at 9:10.

Ideas? What did you put?

I considered just a picture of a cow (ha!), but my boss is a 67 year old man and I thought he might not get it.

As an aside, the lock on my door doesn't work so this sign is the only thing keeping others from walking in!