Is 在瞬间 something like 'at some point'?
I don't think 在瞬间 is used as often as 一瞬间， 瞬间，在那一瞬间，etc, which means at that very moment.

However, I can think of one situation where 在瞬间 can be perfectly used.


  那座桥在瞬间崩塌了。


This sentence means the bridge collapsed in no time. So yes, 在瞬间 means in an instant in this case.

If you can provide more context, I'll be more than happy to follow up.