According to Macmillan these are the synonyms for "a very short period of time"
(noun) a very short period of time
(noun)an extremely short period of time, that ends almost immediately
(noun) an extremely small amount of time
Now to answer the question, I'd have to say "during" is a good enough word to use here however, your intention is to implicitly mention that these conversions take place in an incredibly short amount of time.
There are a couple of ways to do that:
During these conversions, which happen in an instant - under some circumstances data loss happens.
I've used a relative clause to convey that information. You could use other words as well, for instance, in a split second, or in an incredibly short amount of time.
during these split-second conversions- under some circumstances data loss happens.
you could use an adjective as well
in the split second these conversions happen - under some circumstances data loss happens.
you could omit during altogether. (Ludwig)
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