If Empire contract a drilling company like Century, Ensign, Weatherford or Hunt who have rigs in Australia and can get a slot with a sutible rig (which could be very difficult) then tehy could start drilling in 2-3 months. If they try to bring in the Gefco rig from the US IMO it will take at least 6 months to get the rig into Tasmania, set up and certified. Both cases assume that Empire have the financial resources to do this.
If only a few well are going to be drilled then it will be far cheaper to bring an established rig in from the mainland. Running a rig is an expensive business and wages for the crew alone can add up to more than $15,000 a day, fuel can easily cost $1,000 to $3,000 a day depending on the rig. The average dayrate for a rig in Australia is around $35,000 so even if Empire could run their rig for $15,000 a day (which is very unlikley) they would only save around $600,000 per well.