FMA time progression assumptions are as follows.

1) When Edward went back through the gate, he ended up back in London perhaps a few hours after his AU counterpart died.  The gate stripped him once again of his arm and leg.

2) Time moves faster on the AU side of the gate than it does on the FMA side.  If it's suddenly 1921 by the time Al gets searching for his brother again, the ratio is 7-8 AU days per 1 FMA day.  If I went with this time progression the story would be extremely Edward centric and I don't want that to happen.  I'm slowing down the time progression to 2-3 AU days per 1 FMA day so I can do each side justice.