"Back in 5 Minutes" sign
How can I write a small sign that says "Back in 5 minutes" or "Back in a few minutes" that I can put on my office door?
that depends if it should be a polite sentence or not.
If you say it to your family, 五分で戻る、五分で戻りますwould be good.
If you say it politely, like you are a shopkeeper and have to leave your shop few minutes, the expression should be kind of;所用につき少しの間空けさせていただきます。ご迷惑をおかけします。