Learn English – The use of preposition “of”

To a native American English speaker (at least to me), these have different implied meanings:

• decoding time - Can mean how long the decoding process takes, if you write "Decoding time will depend upon..." or when the decoding happens, if you write "At decoding time, ..."
• time of decoding - when the decoding takes place
• data compression - Can refer to the process: "Now performing data compression..." or to the degree of compression: "90% data compression has been achieved using this method."
• compression of data - refers to the process.

When we create phrases of the form "(noun) time", we use the noun as an adjective to describe the time we'll be spending on that noun; we don't say "(noun's) time", which would imply that (noun) was a person who owned that time.

Other examples: Design time, compile time, run time (different from "run-time" or "runtime"), Amok time.

Based on the definition of impression, you'll see that the meaning in this context is a synonym for "the effect", and most definitions recommend the of usage.

It doesn't really make sense to say "the impression about" and whilst you can get an impression from some experience, it depends on the wider context of the sentence.

Given the information provided, I'd suggest you use "the impression of".