Attack Timing

Hi,

I am aware that when two armies combat, one 'battle' takes place every hour. Can I get more information on the specifics of the combat mechanism?

For example, what happens when two units that are attacking merge does the cool-down reset to the time that the second army joins (specifically ranged units)?
Also, what happens to the timing when an order is given? Will a unit that, say, bombards another for half an hour after the last 'battle' and has their target changed, battle in another half an hour, full hour, instantly or randomly?

Cheers,

Moz