Doest the 1 sec offset work on Mirror?

[dda]

...or it's useless? Thank you.

[Cupid]

Yes, you need to have a Mirror subscription before you can change offsets on your snipes. With the free service all snipes are sent with the default 6 second offset.

Personally, I don't recommend shorter offsets, not because they are less reliable but because you tend to get caught out by the bid increment rule more often.
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Mark