Impressions is generally a part of the written record/transcript and includes what the person reading your MRI thinks is going on. It depends on the transcription format and may not be included but most of the time it will be.

As a general rule transcriptions/written records should be in your chart within 48 hours. Now, that isn't always the case as things happen and reports can get behind, but it shouldn't take much longer than that. If it does take longer you can raise cane as it can be argued dangerous to have an incomplete chart.