What does “on the outside” mean?

Question

He will be here in 90 minutes on the outside.

At the outside means "at the most". Is "on the outside" an equivalent expression?

Answer 1

I have never come across such usage. On first look, the sentence seems to convey that "he will be on the outside of this place in 90 minutes".

Answer 2

The only idiomatic meaning of this phrase that I'm aware of is "no longer in prison". Could it mean this in your case? Or maybe the author intended to write "at the outside".

Answer 3

On the outside means away from or not belonging to a particular circle or institution:

when you're on the outside, then you have a much better view of what they're doing.

On the outside could also refer to the external appearance of someone or something.

Is he as honest as he appeared on the outside?

You could be on the outside of a prison's walls or a play ground. But I am not sure how that would fit in your example.

Def. Oxford Dictionary.

Answer 4

The long-established expression is 'at the outside'. However, I think 'at' is falling out of favour these days, more's the pity.

Perhaps the quote in question came from a non-native speaker who is not clear on when to use 'at'. Other languages do not have a preposition that equates perfectly to 'at' so many non-native speakers have difficulty in using it well, or at all.