翻译 我要出去一下，大概20分钟回来

I am going out and will be back in 20 minutes.

I'm stepping out and will be back in about 20 minutes.

这是地道的英语表达

前面I'm stepping out用现在进行时态表示即将进行的动作, 后面用will be back in...表示在...时间后将发生的事情

I'm popping out. 现在进行时表将来。pop out本身就有出去很短时间的意思。
Back in 20 minutes. 主语相同又有上下文，所以省略了I'll be

i will go out for a while ,back in 20 minutes.

I got to go and might be back in 20 mins.

I'll be back in 20 minutes