So I've stumbled across a little reporting roadblock.
In Export, I want to select some month by month reports for comparison.
However, only the Last Month selection copies the month timeframe exactly.
If I use Custom Range to select the month before, I get a weird time selection, probably based on my timezone settings.
See the image.
Manually choosing the last month also selects 'Last Month' so there is no joy in matching up report times by doing that.