What does "insteadly" mean?

Solution 1:

It's not an English word. I don't think it's a mistake either, though. It's more likely to be a jocose usage.

Solution 2:

"Insteadly" is not a standard English word. As others have noted, it appears to be a typo for instantly.

I would think this is probably due the pronunciation of [ˈɪnstəntli] as [ˈɪnstədli] in quick speech, where the hearer has not seen the word spelled before.

EDITED TO ADD: After a Google perusal I see only three usages:

1. This post.
2. Non-native English speakers using it in place of "instantly".
3. Non-native English speaker using it in place of "instead".