Hei Fleso,
Well the good news is that returning back on the 25th from MIA shouldn't be a problem as there are over 100 empty between the 2 flights having said that its a very popular destination so there may be a lot of staff trying .. its too early to know as yet.
On the outbound the 7th looks the best with about 30 empty to MIA and EWR but its still too early to give a better opinion.
I'm guessing that you plan to connect that morning from somewhere in Norway and guess that LGW is not really an option.