Since you play Gythium you play a Revolt world meaning you send in clears to clear the city (1st Round), be sure and have conquest researched in your academy. Once you send your 1st round of attacks be sure and click the "revolt" icon on the attack screen. After you land and if the revolt it successful you will have to wait 12hours before your CS can land and after that first 12hours you have another 12hours to land your CS with additional waves in front of the CS before you will have to re-revolt the city.
CS = Colony Ship (Just Incase)
Ooops..Looks like I got too busy and didn't reply fast enough and someone beat me to it !