WG2Z (5600km) appears to be the last station to spot my 500mW on 10m WSPR today, at 1706z. At the moment I am still spotting USA stations as many are running 5W or more. The band will soon close to the USA and these stations will soon disappear too.
UPDATE 1755z: W4BZW (using 10W) was last spotted at 1734z. The 10m band seems to have closed to the USA and Canada. So, going from 500mW (to an indifferent antenna) to 10W gained just under 30 minutes.
UPDATE 1850z: I spoke too soon. W7CNK (7458km) running 5W was still being copied here at 1846z on 10m WSPR.
UPDATE 1920z: KD4YDD (6717km) was still being spotted at 1918z. No-one is copying my 500mW apart from local G4IKZ (18km)!
UPDATE 2030z: Well I was surprised. W4HFZ (6819km) on the Florida/Georgia border spotted my 500mW WSPR at 1934z and I spotted him immediately before this time. 10m stayed open much later to the USA than I expected today. I think the band is now closed but will continue to monitor and transmit.
UPDATE 2230z: No other stateside spots since W4HFZ above.