Wow Matti
Some great details You got from this day!!
To me it seems the Finnish I-153s was on a very early morning patrol. Perhaps to be over their designated target at dawn. Seems far fetched they were anywhere near the German patrol.
Thanks for stating where Ystinski and Kreivilahti are situated. Seems even less likely they were involved with any fighting in Lavansaari.
As you say, time is always essential, but right now it seems we can rule out friendly fire in this case.
Thanks for sharing your files with us Matti!!
Cheers
Stig