ICAO DOC4444 8.1.1 Longitudinal separation shall be applied so that the spacing between the estimated positions of the aircraft being separated is never less than a prescribed minimum.
At 1210 there is 10 minutes spacing between the positions of the aircraft.
At 1220 the positions of the aircraft have moved by distance based on their GROUNDSPEED. Assuming the GROUNDSPEED is closing like the TAS (and it might not be) the positions of the aircraft will be closer together. You have had less than 10 minutes spacing since 1210, how much less depends on their GROUNDSPEED.
10W, your prop & B763 (they have airports in Iceland?) have 10 minutes until the spacing between the positions of the aircraft is less than 10 minutes.
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I am not an animal, I am an ATC.