Film emulsion fractures easily with thermal shock.
So, in answer to your question - no I'm sure your first couple of seconds at wash water doesn't have to be at 38degC - but it will need to be 38 +/- 2~3C throughout the entire period - including the first couple of seconds.
One hears of many photographers who process their own film complain about grain - most are likely to be suffering from reticulation (fracturing of the film emulsion due to thermal shock)
Hope this helps
Martin
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